Geology Banner

Introduction to Geology

Regional Geology of North America

Getting to know the general geology of a region is useful in many ways. Geologic features such as faults, folds, volcanic intrusions, both modern and ancient, provide the foundation for landscapes. Rock materials that occur in bedrock weather into sediments and soils that influence agricultural uses and their characteristics are important factors in building foundations and infrastructure. Often geologic features have influenced how and where cities have grown, or where major industries have evolved in association with natural resources in a region.

This chapter is an introduction to the major physiographic regions of North America and how they relate to the major population centers of the United States. The science of studying landscapes is called geomorphology (geo- meaning "earth" and -morphology meaning "shape"). A physiographic province is a geographic region with a characteristic geomorphology in which climate and geologic factors over geologic time have given rise to a variety of landforms different from those of surrounding regions. Continents are subdivided into various physiographic provinces, each having a specific characteristics, topographic relief, and physical environments which contributes to its uniqueness.

Figure 1 shows is a general geologic map of North America showing the major physiographic subdivisions. Figure 2 is a legend showing the geologic ages of bedrock used for Figure 1 and most of the other maps presented below. Figure 3 is a generalized summary of geologic history, with important aspects involving the evolution of North America through geologic time.

Click on images for a
larger view.

Physiographic Map of North America
Fig. 1. Major physiographic regions of North America.
Note: maps used in this report are derived (modified) from sources including The North America Tapestry of Time and Terrain (2003) by Kate E. Barton, David G. Howell, José F. Vigil: USGS Geologic Investigations Series map I-2781; and A Tapestry of Time and Terrain (2000) by José F. Vigil, Richard J. Pike, and David G. Howell: USGS Geologic Investigations Series 2720.

Importance of regional physiographic surveys in the history of the United States

As the nation of the United States of America expanded westward in the 19th Century, much of the western region was generally unknown territory. The historic expedition of Lewis & Clark (1804-1806) was intended to map and explore the vast lands acquired by Louisiana Purchase of 1803. The goal was to find a practical route across the western landscape and to establish an American claim to land before other European nations could claim it. Their goal was also to learn about American Indian tribes, and to study the region’s geography, plants, and wildlife. After the Mexican-American War of 1848, the United Stated claimed Spanish Territories encompassing California, most of the Desert Southwest region, and Texas. The addition of these vast territories required many more expeditions to expand the country. Perhaps most significant events was the discovery of gold in the Sierra Nevada foothills which led to the California Gold Rush of 1849—which unleashed perhaps the greatest human migration in its time, and began the extensive exploration efforts to map and exploit the natural resources of the western United States.

Four Great Surveys of the American West

Planning and construction began on the First Transcontinental Railroad in 1863, during the Civil War (1861-1865). It was completed in 1869, connecting the port of San Francisco to the expanding railroad network along the Mississippi and Missouri River in the Midwest. The development of the Western Territories and it mineral resources had become the main focus of national interests. On March 2, 1867, the day after the State of Nebraska was admitted to the Union, Congress enacted legislation to support the United States Geological and Geographical Survey of the Territories. This survey (called the Hayden Survey) focused on the vast region of lands east and within the Rocky Mountains. It was headed by Dr. Ferdinand Vandeveer Hayden who published a series of reports between 1867 and 1883 about the region’s geology, topography, mineral resources, paleontology, and Indian peoples and culture. Also in 1867, Congress authorized Clarence King to lead the first scientific survey of the west (Geological Exploration of the Fortieth Parallel—or the King Survey) to study the geology and natural resources along the 40th parallel, following the general route of the Transcontinental Railroad.

In 1869, Congress authorized American naturalist and civil-war veteran, John Wesley Powell, to lead an expedition to study previously unexplored lands along the Colorado River Basin between Green River. Wyoming and the lower navigable waters of the river below what is now Las Vegas. The Powell Geographic Expedition of 1869 received great acclaim throughout the nation. He repeated his voyage 2 years later to photograph and map the route through the canyon region of the upper Colorado River Basin. Interesting note: the Henry Mountains of south central Utah were the last “undiscovered” mountain range in the United States during the Powell Survey.

Congress also supported the Hayden Geological Survey of 1871-1872. It focused on exploration of the northwestern Wyoming region that lead to the establishment of Yellowstone National Park (established in March 1, 1872, the first National Park).

Army Lieutenant (later Captain) George Montague Wheeler lead early western expeditions in 1869 and 1871 into the west. In 1872 Congress authorized what would be known as the Wheeler Survey with the ambitious task of creating topographic maps of the the lands west of the 100th meridian on scale of 8 miles to an inch (~1:500,000). The Wheeler Survey was tasked to describe everything related to the physical features of the landscape, study the numbers, habits, and dispositions of Indians in the region, select sites for future military installations, gather information for charting future railroads and common roads, and make notes about geology, mineral resources, water, climate, vegetation, and agricultural potential of western lands.

U.S. Geological Survey (USGS)

In 1879, Congress authorized the U.S. Geological Survey and it was given the task to create maps of the country and provide "classification of the public lands, and examination of the geological structure, mineral resources, and products of the national domain." Topographic mapping of much of the populated regions of country was completed on a 1:50,000 scale by the early 20th century, with more detailed 1:24,000 scale mapping (standard topographic maps) formost of the entire US near completion in the 1960s. Today satellite, GPS, and GIS mapping have replaced nearly all "standard" mapping. The current mission of the USGS is to serve "the Nation by providing reliable scientific information to describe and understand the Earth; minimize loss of life and property from natural disasters; manage water, biological, energy, and mineral resources; and enhance and protect our quality of life." Today, the USGS employs thousands of scientists from many natural science disciplines.

Geologic Unit colors by geologic age  used on maps
Fig. 2. Ages of rock units on maps used in discussions.
Geologic time scale with highlights of evolution in earth history
Fig. 3. The geologic time scale (generalized) showing selected highlights in evolution of life on Earth and selected significant events in Earth history leading up to the present.
Physiographic provinces
Fig. 4. Physiographic provinces of the United States
Geologic map of the lower 48 states
Fig. 5. Geologic map of the United States showing state boundaries. Note that most state boundaries cross multiple physiographic boundaries (with the exception of Delaware, Florida, and Louisiana). Each state has its own "geological survey."

Physiographic Regions of the United States

Once the country was "mapped" attempts began to classify landscaped by mutual characteristics: topography, bedrock geology, climate, plants and ecosystems, etc. (Figures 4 and 5). Perhaps the most notable (and widely used) is based on the maps by geologist and geographer, Nevin M. Fenneman (see references). His mapping efforts have been used and modified over the years, but are still very useful for teaching about regional geology and ecosystems. The discussion that follows examines each of the major regions of the United States.
Fenneman, N. M. (1917). Physiographic Subdivision in the United States. Proceedings of the National Academy of Sciences of the United States 3 (1): 17-22.
Fenneman, N. M. (1931). Physiography of western United States. McGraw-Hill.
Fenneman, N. M. (1938). Physiography of eastern United States. McGraw-Hill.

Rocks exposed at the surface throughout North America

Many types of rocks of different ages are exposed at the surface throughout North America. The age and character of the rocks (hardness, chemical composition, etc.) give rise to landscape characteristics and the types of soil and sediments that cover the surface. Figure 6 shows regions where volcanic rocks are exposed at the surface throughout North America. These are regions where volcanic material erupted and accumulated on the surface (both ancient and more recent events). Figure 7 shows the locations where plutonic (intrusive igneous) rocks are exposed at the surface. In comparison to volcanic rocks, the plutonic rocks are typically older, having formed deep in the subsurface by are now exposed after long periods of tectonic uplift and erosion. Figure 8 shows regions where metamorphic rocks are exposed. Like the plutonic rocks, metamorphic rocks are typically ancient and have formed at great depths in the crust, but have been uplifted and exposed by erosion.
Figure 9 shows the extensive regions where sediments and sedimentary rocks are exposed at the surface. These materials typically blanket the surface and overly older rocks of other composition. Sedimentary rocks exposed throughout North America are of all geologic ages and were often deposited in physical environments different that what exists in the region today. What is important is that these rocks of different compositions and ages give rise to the fundamental characteristics of the different physiographic provinces.
Volcanic rocks exposed in North America Plutonic (Intrusive Igneous) Rocks exposed in North America Metamorphic Rocks exposed in North America Sediments and Sedimentary Rocks cover of North America
Fig. 6. Volcanic rocks exposed in North America. Fig. 7. Plutonic rocks (intrusive igneous rocks) of NA. Fig. 8. Metamorphic rocks of North America. Fig. 9. Sediments and sedimentary rocks of NA.

Canadian Shield

The Canadian Shield encompasses the most extensive region of North America and is host to most of the oldest rocks on the continent. (see Figure 1). The Canadian Shield dominates all of eastern Canada. Hudson Bay is located at the center of the Canadian Shield region. It is bounded on the north and east by the Arctic Archipelago region and by Greenland and the North Atlantic Ocean. On the south the Canadian Shield is bounded by the Great Lakes and the St. Lawrence River Valley region. The character of the Canadian Shield's landscape is highly influenced by the scouring erosion of moving ice of the Laurentide Ice Sheet that covered most of Canada during the Pleistocene ice ages (Figure 10). Continental glaciers stripped off the sedimentary cover that may have covered much of the region before the ice ages. As a result ancient igneous and metamorphic rocks are exposed at or near the surface and are host to the many important metals and strategic mineral deposits mined in eastern Canada (Figure 11).

Although the bedrock in the Canadian Shield is extremely old—having formed roughly more than 2 to 3 billion years ago in mountain ranges and small landmasses crushed together by plate-tectonic forces. However, those ancient mountain ranges eroded away long ago, and the crust in the region has grown thinner, and sits isostatically lower that other younger, thicker crust in the surrounding province regions (Figure 12). However, because of the geologically recent glaciations, the Canadian Shield displaces a relatively chaotic surface appearance, having numerous lakes and "deranged" river drainage patterns on the recently glaciated landscape.

The Superior Lowlands Province are part of the Canadian Shield that extends into the United States around the western end of Lake Superior (see Figures 4 and 5), encompassing part of Minnesota, upper Michigan and Wisconsin. Ancient igneous and metamorphic rocks are exposed in what are called the Iron Ranges where belts of ancient banded-iron formation deposits are exposed and have been extensively mined to provide iron ore shipped to steel mills throughout the easter Great Lakes region. The timbered and rocky shorelines in the Superior Lowlands Province are host to the Apostle Islands National Lakeshore and Voyageurs National Park.
Continental glacial cover at the peak of the Last Ice Age Map showing locations of igneous rocks exposed at the surface throughout North America
Fig. 10. The Laurentide Ice Sheet blanketed the entire Canadian Shield Region. Fig. 11. Ancient igneous rocks (volcanic & plutonic) dominate the Canadian Shield.
Formation of the Canadian Shield Aerial view of Voyageurs National Park area
Fig. 12. The Canadian Shield is the ancient core of the North American continent. Fig. 13. This aerial view of Voyageurs National Park shows typical landscape character of the Superior Lowlands Province.

Atlantic and Gulf Coastal Plains and Continental Shelf

All continents have coastal plains created by erosion associated with the rise and fall level through geologic time. Coastal plains are the exposed equivalent of continental shelves. When continental glaciers form, sea level falls as precipitation is trapped on land as ice, causing sea level to fall, exposing the continental shelves. As continental glaciers melt, sea level rises (as is currently happening since the end of the last ice age, about 11,000 years ago). During the peak of the last ice age sea level was as much as 120 meters (400 feet) lower than it currently stands and the coastal plains extended seaward to the shelf break at the edge of the continental margins.

In addition, coastal plains (and continental shelves) are associated with thick blanket of sediments that have accumulated along the margin of continents. These wedges of sediments grow increasing thicker seaward and are formed from sediments eroded from land or accumulated as massive organic reef deposits formed in warm, shallow marine environments. For instance, the Florida Platform is underlain mostly by limestone and carbonate-rich sediments deposited in shallow marine environments when sea level was higher than today (Figure 14).

The Atlantic Coastal Plain and Gulf Coastal Plain are extensive because they are on the passive margin of the North American Continent (Figure 15). The sediments of the coastal plains have been accumulating since North America split away from the supercontinent Pangaea, starting about 200 million years ago. As the Atlantic Ocean basin opened, large quantities of sediments were shed from the eroding remnants of the ancestral Appalachian Mountains (discussed below), slowly building a thick wedge of sediments along the continental margin as the Atlantic Ocean Basin slowly expanded.

The western edge of the Atlantic Coastal Plain is marked by the "Fall Line" (Figure 16). The fall line is an imaginary line that basically marks the boundary where rivers draining from the Appalachian uplands descend onto the coastal plain become deep enough to be navigable by ocean-going ships. Most of the major cities in the eastern United States developed at the points where ships traveling up river valleys could stop to load/unload their goods. The fall line basically follows the ancient coastline when the Earth was last completely ice free (about 33 million years ago), before glacial ice began to accumulate in Antarctica, Greenland, and other glacial regions of the world. Since then sea level has risen and fallen many times, flooding and then re-exposing the coastal plain region many times.

The Mississippi Embayment is an extension of the Gulf Coastal Plain that extend northward into the greater Mississippi River Valley all the way to Cairo, Illinois (Figure 18). The coastal plain sediments of Late Cretaceous and younger ages lie unconformably on top of an eroded surface of more ancient bedrock of the Appalachian Mountains to the east and the Ouachita Mountains to the west. Along the border of the Mississippi Embayment, Cretaceous-age coastal marine sediments (called the Selma Formation) weather to produce the rich soils along a belt of land (including Selma, Alabama) that is famous for cotton farming and was a major economic region of the American South before the Civil War.

Florida continental shelf Continental margin showing geology of coastal plane and continental shelf sediments
Fig. 14. The Florida Peninsula is an exposed portion of a larger shallow shelf platform (shown in red—less than 200 meter deep). Fig. 15. Diagram of a continental margin showing the relationship of the coastal plain, continental shelf, and shelf margin.
Fall Line Pine Barrens of New Jersey as seen from Apple Pike Hill
Fig. 16. The "Fall Line" generally marks the western boundary of the Atlantic Coastal Plain. Fig. 17. The Pine Barrens of New Jersey is a region that illustrates a natural landscape on the Atlantic Coastal Plain.
Mississippi Embayment Hurricane Katrina as seen from space
Fig. 19. Hurricanes play a major role in shaping the landscapes along the Gulf and Atlantic coastal plains. They redistributed sediments deposited by rivers and reshape the shorelines. This view shows Hurricane Katrina (2006) as it came onshore, causing the most costly natural disaster in US history in its time.
Fig. 18. Map showing the Mississippi Embayment, an extension of the Gulf Coastal Plain that extends northward into the Mississippi River Valley to Cairo, Illinois.
Examples of National Parks located on the Atlantic and Gulf Coastal Plains (from north to southwest):

Fire Island National Seashore, Long Island, New York
Gateway National Recreation Area, New York and New Jersey
Assateagure Island National Seashore, Maryland
Cape Hatteras National Seashore, North Carolina
Biscayne National Park, Florida
Everglades National Park, Florida
Padre Island National Seashore, Texas
Memphis, Tennessee
Fig. 20. Bridge over the Mississippi River in Memphis, Tennessee, part of the Mississippi Embayment.

Appalachian Mountains Provinces

The Appalachian Mountains encompass a vast region along the eastern United States extending from Alabama and Georgia (to the south) to New England and eastern Canada (to the north). The Appalachian Mountains are an ancient range of mountains that formed as North America collided with Africa, Europe, and other smaller landmass that eventually assembled to form the supercontinent of Pangaea in Late Paleozoic time. The Appalachian Mountains may have rivaled the modern Himalayan Mountains in their size and extent at the peak of their orogenic formation in the Late Paleozoic Era. Today, the region is still very mountainous and hosts deeply eroded plateau regions. The region is subdivided into 5 physiographic Provinces (Figures 21 and 22):

* Piedmont Province
* Blue Ridge Mountains Province
*Valley and Ridge Province
*Appalachian Plateaus Province
* Northern Appalachians Province (or New England Province).


Each of these physiographic provinces are discussed below.

Appalachian Mountain Provinces Southern and Central Appalachian Mountains
Fig. 21. Map showing the physiographic provinces of the Appalachian Mountains region. Fig. 22. General geologic map of the southern and central Appalachian Mountains region.

Piedmont Province

The Piedmont Province is perhaps best described as the eastern foothills region of the greater Appalachian Mountains. The Piedmont is bounded on the east by the Atlantic Coastal Plain and on the west by the higher mountain ridges of the Blue Ridge Mountains in the south and the higher mountain ridges of the Valley and Ridge Province to the north. The Piedmont extends from Alabama at the south to the Hudson River (New York/New Jersey border area) in the north (Figures 21 and 22). The Piedmont region is characterized by gentle rolling hills, roughly between about 200 to 1000 feet in elevation, mostly forested. The geology of the Piedmont is complex, preserving rocks formed over a billion years through several major mountain-building periods including the Grenville Orogeny in Late Precambrian time. Upheavals throughout the Paleozoic Era resulting in the formation of the Appalachian Mountains and the formation of Supercontinent Pangaea, and then the subsequent rifting as Pangaea as it broke apart in the Mesozoic Era.

A series of rift basins formed and filled in with lava flows and sediments eroding from surrounding mountain regions. These ancient rift valleys are called “Mesozoic Basins” (Figure 23). Sediments and volcanic rocks that filled these basins are mostly of Triassic age (some early Jurassic). A series of Mesozoic-age ancient rift valleys exist along the East Coast from Newfoundland to North Carolina, including the Connecticut River (or Hartford) Basin, Newark Basin (New Jersey-Pennsylvania), Gettysburg Basin (Pennsylvania), Culpepper Basin (Virginia and Maryland), Richmond Basin (Virginia), and Deep River Basin (North Carolina). Other Mesozoic basins exist under the sedimentary cover of the Coastal Plain. These basins formed as ancient supercontinent Pangaea split apart, but only the Atlantic rift basin continued to form into the Atlantic Ocean basin. Perhaps a most famous geologic feature is the Palisades, a wall of diabase (basaltic) volcanic rocks that crops out along the east side of the Hudson River in New Jersey across from New York City (Figure 24).Triassic-age red-beds crop out throughout the Newark Basin (Figure 25).

Mesozoic Basins of the Piedmont Province in the Eastern United States.
Fig. 23. Mesozoic Basins of the Piedmont Province in the eastern United States.

Major cities located within the Piedmont (along the Fall Line with Coast Plain) include Philadelphia, Baltimore, Washington DC and the Atlanta metropolitan areas (see Figure 16).
Palisades, a volcanic sill of Northern New Jersey along the Hudson River across from Manhattan (New York City). Triassic-age red-beds (strata) crop out along the Delaware River in the Newark Basin along the New Jersey/Pennsylvania border. The rolling landscape along the Potomac River in the region around Washington DC is typical of the Piedmont physiography. Great Falls of the Potomic River on the Virginia-Maryland border.
Fig. 24. The Palisades, a volcanic sill of Late Triassic age located in northern New Jersey along the Hudson River across from New York City. Fig. 25. Triassic-age red-beds (strata) crop out along the Delaware River in the Newark Basin along the New Jersey/Pennsylvania border. Fig. 26. The rolling landscape along the Potomac River in the region around Washington DC is typical of the Piedmont physiography. Fig. 27. Great Falls of the Potomac River on the Virginia-Maryland border is located in the Piedmont region.

Blue Ridge Province

The Blue Ridge Mountains get their name from the typically bluish haze produced by natural aerosol compounds, isoprenes, that are released by trees in the southern Appalachian region—also the “smoky” applied to the Smoky Mountains. The Blue Ridge Mountains are a narrow band of a high mountainous ridges or a single high ridge that extend from southern Georgia northward into Pennsylvania. In geologic terms, the Blue Ridge forms the distinct eastern margin of the Southern Appalachian Mountains (Figure 28). For most of its length, the Blue Ridge rises high above the Piedmont lowlands to the east and the Great Appalachian Valley to its west (part of the Valley and Ridge Province). The highest mountain in the eastern United States, Mt. Mitchell (elevation 6,684 feet) is located in the southern Blue Ridge Mountains of North Carolina. More than 120 peaks in the Blue Ridge Mountains rise above 5,000 feet.

For most of its length, the Blue Ridge Mountains are parklands including the Great Smoky Mountains and Shenandoah National Parks, connected by the scenic Blue Ridge Parkway and the Appalachian Trail for most of its length (Figures 29 to 32).

Ancient metamorphic rocks exposed in the Blue Ridge formed from deep crustal compressional forces associated with the landmass collisions associated with the Grenville Orogeny, a regional metamorphism event associated with mountain building in Late Precambrian time, a little more than a billion years ago). These rocks exposed along the Blue Ridge consists of complex folded metamorphic rocks, mostly granitic gneiss (derived from more ancient volcanic and sedimentary rocks). The Blue Ridge began to rise in Silurian time (about 400 million years) and an erosional remnant of a much greater mountain range that formed in the middle to late Paleozoic Era as the North American continental landmass collided with Europe, Africa, and other smaller landmasses that assembled together to form the supercontinent Pangaea. At the peak of the Appalachian Orogeny (or Allegheny Orogeny) in Pennsylvanian to early Permian time (about 325 to 260 million years), the mountains would have rivaled the modern Alps is size and extent. Across North America. Sediments shed from the mountains flooded westward accumulating in the Appalachian Plateau region and regions further west (discussed below).

Generalized cross section of the Appalachain Mountains and Appalachian Basin.
Fig. 28. Generalized cross section of the southern Appalachian Mountains region.
National Parks located in the Blue Ridge Mountains include:

Shenandoah National Park (Virginia)

Blue Ridge Parkway
(North Carolina and Virginia)

Great Smoky Mountains National Park
(North Carolina, Georgia, and Tennessee)
View of Great Smoky Mountains National Park National Park from Klingman's Dome, Tennessee. View of the southern Appalachian Mountains from the Blue Ridge Mountains along the Blue Ridge Parkway in North Carolina. Linville Falls in North Carolina is along the Blue Ridge Parkway. Fall colors along the Blue Ridge in Shenandoah National Park, Virginia.
Fig. 29. View of Great Smoky Mountains National Park as seen from Klingman's Dome, Tennessee. Fig. 30. View of the southern Appalachian Mountains from the Blue Ridge Mountains along the Blue Ridge Parkway in North Carolina. Fig. 31. Linville Falls in in upper Linville Gorge, a scenic area in North Carolina is along the Blue Ridge Parkway. Fig. 32. Fall colors along the Blue Ridge in Shenandoah National Park, Virginia.

Valley and Ridge Province

The Valley and Ridge Province is a subdivision of the greater Appalachian Mountains. It is a broad, mountainous region east of the Blue Ridge Mountains and extends from upstate New York to Alabama, and is bounded on the west by the Appalachian Plateaus Province. Parallel to the western side of the Blue Ridge is the Great Appalachian Valley. The western side of the Valley and Ridge Province, the Allegheny Front (an escarpment) marks the western boundary with the Appalachian Plateaus Province. The Valley-and-Ridge Province is characterized as a series of ridge lines and intervening valleys that reflect the erosional characteristics of rock layers that have been folded and thrust faulted into complex structures, mostly anticlines and synclines, very similar to folds in a carpet that has been pushed up against a wall (Figure 33). Sedimentary rocks exposed throughout the Valley and Ridge are part of the Appalachian Basin, a thick sequence of sedimentary deposits that represented the continental margin basin deposits before continents assembled to form supercontinent Pangaea.

During the Allegheny Orogeny in Late Paleozoic time, the North American Plate was colliding with the African Plate. The upper layers of the crust, composed mostly of layers of sedimentary rock, was shoved westward, creating a series of northeast-southwest-trending structural folds. Erosion over the last 200 million years have stripped away thousands of feet of overlying sediments, exposing the folds and complex structure we see today. Unlike rocks of the Piedmont and Blue Ridge, rocks of the Valley and Ridge Province have experiences minimal metamorphism. However, harder, erosion-resistant rock layers from ridges and softer layers erode to form valleys. In many cases, the the axis of anticlines are now valleys and axis of synclines are now ridges (Figures 33-36). The ancient age of the landscape is reflected by the unusual river systems that cut across the ridge lines. The Delaware, Susquehanna, New, and Potomac Rivers all drain eastward and cut through the Valley and Ridge region. These rivers probably flowed eastward across unconsolidated sediments that covered the region in the geologic past when there was little topographic relief and before the region was later uplifted to its current elevations. The result is that the rivers cut through “water gaps” that are perpendicular to the hard strata that form the ridges (Figure 35).

Historically, the parallel series of ridges and valleys created problems for the growing nation of the United State to expand westward. Land travel westward in the age of walking or riding horses was hindered by the seemly endless number of ridges in the region. Even today, the region is sparsely populated compared to the lowland regions east and west of the Appalachians. Cumberland Gap is the only low pass in the Cumberland Mountains, a long up-thrusted ridge over a hundred miles long located of along the western margin of the Valley and Ridge Province along the border of Kentucky, Tennessee, and West Virginia. In the late 1780s and 90s, a crew lead by explorer Daniel Boone constructed the Wilderness Road through Cumberland Gap as the first overland wagon road for settlers moving westward across the Applachian Mountains into Kentucky and the Ohio River Valley region.

The Hudson River Valley in New York roughly defines the northern boundary between the Taconic Mountains (to the east) and Catskill Mountains (to the west)(Figure 36). The Taconic Mountains are folded and faulted similar to the Valley and Ridge, but are more ancient (and are included in the New England Province). The Catskills are the northern end of the Appalachian Plateaus Province.
Satellite view of the Harrisburg, Pennsylvania region showing the folded layers of the Valley and Ridge Province (top) and Piedmont (bottom). Syncline on a ridgeline exposed along a cut in I68 in western Maryland. The Delaware Water Gap is where the Delaware River cuts through Kittatinny Mountain, a ridge in the northern Valley and Ridge Province (New Jersey and Pennsylvania). Generalized cross section of the Hudson River Valley region with fold-thrust belt of the Taconic Mountains east of the Catskills, NY. .
Fig. 33. Satellite view of the Harrisburg, Pennsylvania region showing the folded layers of the Valley and Ridge Province (top) and Piedmont region (bottom). Fig. 34. An inverted geologic paradox: a syncline that is now a ridge line, is exposed along a cut in Sideling Hill along I-68 in western Maryland. Fig. 35. Delaware Water Gap NRA is where the Delaware River cuts through Kittatinny Mountain, in the northern Valley and Ridge Province in New Jersey and Pennsylvania. Fig. 36. Generalized cross section of the Hudson River Valley region with fold-thrust belt of the Taconic Mountains east of the Catskills Mountains in New York.

Appalachian Plateau Province

The Appalachian Plateau Province is the northeastern side of the greater Appalachian Mountains region (or the Appalachian Basin, the thick underlying sedimentary basin that underlies the Appalachian Mountains region). The Appalachian Plateau Province extends from Alabama to New York (see Figures 21 and 22). The province is subdivided into several separate plateau regions including the Cumberland Plateau (Tennessee-Kentucky), Allegheny Plateau (West Virginia-Pennsylvanian-Ohio), Catskills and Pocono Mountains (New York-Pennsylvania), and Mohawk Plateau (in the Finger Lakes region in upstate New York). These mountainous regions are actually erosionally dissected plateaus, having ridge lines that basically have generally similar elevation throughout. The eastern sides of each of these regions are characterized by a high escarpments that borders the Valley and Ridge Province. The Catskills-Mural Front is a steep escarpment on the east side of the Catskills, overlooking the Hudson River Valley (Figure 36). The Allegheny Front is an east facing escarpment along the Allegheny Mountains in Pennsylvania, Maryland, and West Virginia, and the Cumberland Mountains of southeastern Kentucky form an east-facing escarpment bordering the Valley and Ridge region of western Virginia and eastern Tennessee.

Three mountain-build episodes in the Paleozoic Era resulted in the formation of great regional delta systems that spread westward onto the North American mid continent. These mountain-build periods include the Taconic Orogeny (Ordovician-Silurian time), Acadian Orogeny (Devonian), and Allegheny Orogeny (Pennsylvanian-Permian) (Figures 37 and 38). These orogenies are associated with collisions of smaller landmasses that accreted onto the North American continental margin and the eventual collisions of Africa, Europe, and North America to form the supercontinent Pangaea at the end of the Paleozoic Era. The bedrock of the adjacent Appalachian Plateaus consist of a series of overlapping “clastic wedges” associated with ancient delta systems of rivers that drained from the mountainous highlands that existed to the east along what is now the Atlantic continental margin region (Figure 39).

The ancient delta systems on the western side of the ancestral Appalachian Mountains spread westward, forming broad swamplands and river floodplains that spread into shallow inland seas that covered much of the midcontinent region throughout the Paleozoic Era. These ancient delta-swamplands deposits are host to the extensive coal fields of Pennsylvanian age throughout the Appalachian Plateau region. Deposits from ancient river delta and coastal plains along the interior shallow seaways are host to the coal fields of West Virginia, Kentucky, Indiana, Illinois, and as far west as Missouri and eastern Kansas. Sandstone beds of Pennsylvanian age cap the Cumberland Plateau region, and are well exposed in the Red River Gorge National Geologic Area, Kentucky (Figure 40).

Evolution of the Northeastern US region Breakup of Pangaea in Mesozoic to Cenozoic time and formation of the Newark and Atlantic Ocean basins.
Fig. 37. Paleozoic mountain-building periods include the Taconic, Acadian, and Allegheny orogenies, leading to formation of Pangaea. Fig. 38. Breakup of Pangaea and formation of the modern Atlantic Ocean and the passive continental margin in Mesozoic and Cenozoic time.
Clastic wedges (ancient delta systems) associated with orogenies that provided sediments to  the Appalachian Plateaus Province. Red River Gorge is incised into the Cumberland Plateau in southestern Kentucky
Fig. 39. Clastic wedges (ancient delta systems) associated with orogenies that provided sediments to the Appalachian Plateaus Province. The ancient deltas expanded westward filling in shallow seaways in the North American midcontinent region. Fig. 40. Red River Gorge is incised into the Cumberland Plateau in southeastern Kentucky (central part of the Appalachian Plateaus). Conglomeratic sandstones form the caprock throughout the entire Applalachian Plateaus region.

Northern Appalachians (New England Province)

The New York City metropolitan region, home to nearly 25 million people, is uniquely located at the intersection of several physiographic provinces. Southern New Jersey is part of the Coastal Plain Province (Figure 41). Long Island is formed from the terminal glacial moraines of the Late Pleistocene (Wisconsinian) continental glaciers that overly buried coastal plain deposits. The Highlands of northern New Jersey and Connecticut, and the island of Manhattan are metamorphic rocks that geologically part of the New England Province (and similar to the Piedmont except the region was glaciated). East of the Hudson River the bedrock consistsof Triassic to Early Jurassic sediments and volcanic rocks of the Newark Basin (a Mesozoic Basin). Nearby in northern New Jersey Highlands and along the Hudson Valley are folded and thrust-faulted sedimentary rocks of early Paleozoic Age (Valley and Ridge Province), and flat-lying sedimentary rocks of the Catskills and Pocono Mountains (New York and Pennsylvania) are part of the Appalachian Plateau Province.

The New England Province shares many of the same physiographic characteristics of the Piedmont and Blue Ridge (Figure 42). The province also share a similar complex geologic history with mountain building episodes associated with the Taconic, Acadian, and Allegheny orogenies (see Figure 37). One significant difference is that the entire region was covered by the Laurentide continental glaciers repeatedly throughout the Pleistocene Epoch. The White Mountains of Vermont and New Hampshire share a similarity with the Blue Ridge Province, both consisting of Grenvillian granitic metamorphic rocks of Precambrian Age (Figure 43).

Mt. Washington, elevation 6,288 feet (1,917 m) is the highest mountain in New England, and is famous for having the highest wind-gusts records for the world for many decades. Mt. Washington is one of the high peaks of the Presidential Range, a series of peaks named after American presidents. The Taconic Mountains are a fold-thrust belt (similar to the Valley and Ridge region) that runs north-to-south along east side of the Hudson River Valley. The Hudson River itself is a fjord, a submerged glaciated river valley.
Both Long Island and Cape Cod, and the islands of Marthas Vineyard and Nantucket consist of surficial deposits of glacial moraines and outwash deposited by continental glaciers (Figure 45).
Geology of the New York City Region
Fig. 41. Geologic map of the New York City region, a region that encompasses parts of several provinces in relatively close proximity Learn more at Geology of the New York City Region (USGS website).
New England and Northern Appalachians View of the White Mountains region of New Hampshire as seen from the Appalachian Trail, New Hampshire. Connecticut River Valley. Cape Cod, a hook-shaped peninsula formed from reworked glacial deposits, with Marthas Vineyard (below), Massachusetts.
Fig. 42. The New England Province consists of many elements similar to the Piedmont and Blue Ridge Provinces, except that the region was covered by continental glaciers. Fig. 43. View of the Presidential Range in the White Mountains region of New Hampshire and Vermont as seen from this view along the Appalachian Trail. Fig. 44. The Connecticut River flows south through a Mesozoic basin that bisects older rocks of the Connecticut Highlands of the New England Province (Northern Appalachians). Fig. 45. Cape Cod, a hook-shaped peninsula in Massachusetts, with Martha's Vineyard (island below and left) formed from (and reworked from) Pleistocene glacial deposits.

Adirondack Mountains Province

The Adirondack Mountains is a large dome-shaped uplift, about 160 miles wide with more than 100 peaks distributed through the region (Figure 46). The bedrock is more than a billion years old, formed during the Grenville Orogeny in Late Precambrian time (Proterozoic). Metamorphic rocks, once buried many miles in the crust. Unusual rocks including anorthosite and marble are now exposed; minerals mined in the region include garnet, graphite, wollastonite, graphite, magnetite, and hematite. In contrast, the dome itself is very young—rising in the region starting about 5 to 10 million years ago. The region has risen nearly 7,000 feet with erosion stripping away the sedimentary cover. The mountain region is still rising.

The Adirondack Mountains were overrun by the Laurentide glaciers of the Pleistocene Epoch that moved south out of Canada. The glaciers stripped away the sedimentary cover. Late in the Pleistocene as the great continental glaciers restricted, alpine glaciers continued to shape the landscape, creating features including horns, cirques, U-shaped valleys, and other glacial features.

Algonquin Peak
Fig. 46. Algonquin Peak is one of the highest peaks in the Adirondack Mountains in upstate New York.

Great Lakes and the St. Lawrence Valley Province


St. Lawrence Valley Province

The St. Lawrence River is the primary drainage form the entire Great Lakes region. The St. Lawrence Valley Province is a lowlands region along the St. Lawrence River between glacial Lake Ontario and where the river becomes a tidewater estuary near Quebec City (the Gulf of St. Lawrence is one of the largest estuaries in the world). The valley includes parts of northern New York and parts of southern Ontario and Quebec. The province is flanked on the south by the Adirondack dome and uplands of the southern Canadian Shield to the north. The elevation ranges slopes gently from about 1000 feet in the west to about 80 feet in the east, but consists mostly of gentle rolling hill country. The bedrock consists of sedimentary layers (Ordovician shale and limestone, and Cambrian sandstone) with a veneer of glacial deposits. These deposits overlie Proterzoic Grenvillian metamorphic rocks similar to the Adirondack region. The Canadian cities of Montreal and southern Ottawa are within the province.



The Great Lakes

The Great Lakes are five interconnected freshwater lakes in the midwestern United States and Canada. The lakes drain eastward, connected to the Atlantic Ocean through the Saint Lawrence River (Figure 47). Lake Superior (elevation 591 feet) is the largest lake in the world—it is also the deepest of the lakes, averaging about 500 feet deep with the deepest point at 1,332 feet. Lake Michigan (the second largest), and is connected with Lake Huron (the third largest). Lake Michigan and Lake Huron have an average elevation 577 feet. The Detroit River connects Lake Huron to Lake Erie (a distance of 28 miles). Lake Erie (the fourth largest) has an average elevation of 571 feet. Lake Erie drains into the Niagara River and into Lake Ontario (the fifth largest, elevation 243 feet). Niagara Falls is on the Niagara River between Lake Erieand Lake Ontario (Figure 48). Lake Ontario drains into Saint Lawrence River. The Great Lakes formed as the last continental glaciers retreated northward about 14,000 years ago. The lake basins were carved by advancing ice sheets through the Pleistocene Epoch, scouring away the sedimentary cover over the Precambrian basement rocks and depositing the material as moraines and glacial till in the midwestern states to the south.
The Great Lakes form the natural boundary between the Canadian Shield and the Mid Continent region of the United States.
Fig. 47. The Great Lakes form the natural boundary between the Canadian Shield and the Mid Continent region of the United States.
Aerial view of Niagra Falls on the Niagara River between Lake Erie and Lake Ontario near Buffalo, New York.
Fig. 48. Aerial view of Niagara Falls on the Niagara River between Lake Erie and Lake Ontario near Buffalo, New York.

Mid-Continental Regions of the United States

In contrast to the regions along the East Coast and the Rocky Mountains and western states, the physiographic features and geology of the midcontinent region is relatively simple by comparison. Physiographic subdivisions are based on subtle differences in geology and climate.

Interior Low Plateaus Province

The Interior Low Plateaus Province extends from the the Greater Cincinnati metropolitan region in the Ohio River Valley southward to the Nashville Region of central Tennessee (Figure 49). The province is characterized by low rolling hills and plains, and river valleys. Elevations in the region range from a low of 380 feet (along the Ohio River in Louisville, Kentucky) to about 800 to 1,200 feet in upland areas.

In geologic terms, the Interior Low Plateaus region consists a broad structural upwarp that roughly parallels the Appalachian Plateau region to the east. The region is underlain by nearly flat-lying sedimentary rocks of Ordovician to Mississippian age. Layers of Ordovician limestone and shale are exposed along the crest of two broad dome upwarps: the Cincinnati Arch (including parts of southwestern Ohio, Kentucky and southwestern Indiana) and the Nashville Dome in central Tennessee.

The Cincinnati Arch is also called the Bluegrass region where Ordovician sedimentary rocks are exposed at the surface. The Bluegrass region named for a natural species of "bluegrass" in the region). The Inner Bluegrass is a sub region where Middle Ordovician-age rocks are exposed in the region around Lexington, Kentucky (Figure 50). A high phosphorus content in the Middle-Ordovician-age Lexington Limestone in the Inner Bluegrass region makes it ideal for agriculture, particularly raising thoroughbred horses, making is one of the most valuable (and expensive) agricultural regions of the world (Figures 51 and 52).

The Ohio River roughly marks the southern boundary of the Laurentide continental glaciers. At the peak of the Ice Ages, large lakes, perhaps larger than the modern Great Lakes, existed south of the ice sheet, flooding the large portions of the Interior Lowlands. Lakes filled and spilled over divides, and great floods carved canyons that eventually became the path of the Ohio River.
Central Lowlands Cincinnati Arch
Fig. 49. Physiographic provinces of the Midwest. Fig. 50. Dome structure of the Cincinnati Arch region.
Flat-lying layers of Late Ordovician limestone and Shale crop out throughout the Cincinnati region, Ohio, Kentucky, and Indiana. The Kentucky River Gorge cuts through Middle Ordovican age strata  the Inner Blue Grass region of Kentucky.
Fig. 51. Flat-lying layers of Late Ordovician limestone and Shale crop out throughout the Cincinnati region (Ohio, Kentucky, and Indiana). Fig. 52. The Kentucky River Gorge cuts through Middle Ordovician age strata the Inner Blue Grass region near Lexington, Kentucky.

Central Lowlands Province

The Central Lowlands Province include the parts of majority of the Midwestern States: Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Missouri, Ohio, Oklahoma, and Wisconsin. For most of the region, the landscape is a low mostly flat plain or low rolling hills cut by stream valleys. The region north of the Ohio and Missouri rivers was impacted by continental glaciers. The region is the also called the "Corn Belt" because nearly the entire region is utilized for agriculture.

The region is underlain by generally flat-lying sedimentary rocks with some anomalously larger structural basins that formed slowly and filled in with sediments throughout the Paleozoic Era. These include the Michigan Basin (encompassing most of the lower Michigan Peninsula between Lake Michigan and Lake Huron), the Illinois Basin (in southwestern Indiana and southern Illinois and Western Kentucky, and the Forest City Basin (extending from southern Iowa, eastern Kansas, western Missouri, and into Oklahoma) (see Figure 49). Compared with structural basins elsewhere in the west, these basins are relatively shallow—filled with several thousands of feet of sedimentary deposits. The center of these basins are capped with with coal-bearing sedimentary deposits that form cliffy sandstone escarpments in belts around portions of the basins. The Pennsylvanian sandstone layers form escarpments s that overly a thick sequence of Mississippian-age limestone formations that underlie the entire region (Figures 53 and 54). These limestones are host to the famous and extensive cavern systems in Kentucky, Indiana, and Missouri, including those in Mammoth Cave National Park.

The region is drained by the principle tributaries: the Ohio River and the Missouri River merge with the Mississippi River near St. Louis, forming the principle river drainage of the mid continent (Figures 57 and 58). Prior to the ice ages, rivers in the region may have drained northward toward Hudson Bay. The continental glaciers blocked the rivers, creating lakes that would fill and eventually breach into the next valley. The drainages consolidated into the Mississippi River system. The Mississippi Embayment region filled with sandy glacial outwash sediments, creating the extensive aquifer system in the lower Mississippi Valley.

Physiographic regions of Kentucky
Fig. 53. Physiographic regions of Kentucky.
The Dripping Springs escarpment in Mammoth Cave National Park in Kentucky.
Fig. 54. The Dripping Springs Escarpment of the Pennyroyal Plateau along the Green River in Mammoth Cave National Park in western Kentucky. The caverns are in Mississippian-age limestones.
Typical view of Indiana corn fields. Mississippi River in Wisconsin Confluence of the Misouri, Illinois, and Mississippi Rivers near St. Louis as viewed from satellite during floods of 2008. Satellite view of the confluence of the Mississippi and Ohio Rivers near Cairo, Illinois.
Fig. 55. An Indiana corn field represents a typical view of the landscape practically anywhere in the Central Lowlands Province of the Midwestern US. Fig. 56. View looking east from an escarpment along the western side of the Mississippi River looking toward the lowlands of southern Wisconsin. Fig. 57. Confluence of the Missouri, Illinois, and Mississippi Rivers near St. Louis as viewed from satellite during floods of 2008. Fig. 58. Satellite view of the confluence of the Mississippi and Ohio Rivers near Cairo, Illinois. Note the sediment color contrast of the two rivers.

South-Central Interior Region of the United States

The south-central interior of the United States (between the Central Lowlands and the Coastal Plain) includes the Ozarks region of parts of Missouri, Arkansas, and northeastern Oklahoma. This region is a dominantly forested and hilly that gradually transitions to the open grasslands of the Great Plains to the west and the pinelands to the south in east Texas. A series of escarpments, plateaus, and uplifts extend across the central and west Texas between the Coastal Plain and the southern High Plains of the "panhandle" regions of Texas and Oklahoma.

The regional geologic history is influenced by the Ouachita Orogenic Belt, a regional mountain belt similar in age and origin to the Appalachian Mountains (Figure 59). The Ouachita Orogenic Belt is only physically expressed on the surface in the region in the Ouachita Mountains and the Marathon Mountains in West Texas. Elsewhere, the Ouachita Orogenic Belt is hidden, buried beneath younger sedimentary cover of the Mississippi Embayments, the Gulf Coastal Plain, and plains of Central and West Texas. Two other mountain regions include the Arbuckle Mountains and Wichita Mountains of southern and western Oklahoma.
Geologic map of Texas region
Fig. 59. Geology and physiography of the South-Central United States region.

The Ozark Plateau Province

The Ozark Plateau Province is encompasses portions of Missouri, Arkansas, and eastern Oklahoma. The Ozarks region is characterized by erosionally dissected plateaus with steep valley walls and narrow river bottoms. The region is mostly covered with shrub-oak forests. The Ozarks is subdivided into four general regions based on elevations and bedrock characteristics (Figure 60).

The St. Francis Mountains of Missouri is a region where crystalline basement rocks are locally exposed through the sedimentary cover of the greater Mid continent region. These rocks are Precambrian age (about 1.5 billion years) and consist of a mix of granitic and metamorphic rocks. The St. Francis Mountains are within the large Ozark Plateau region. All the other rocks in the Ozarks region are sedimentary formations of Ordovician to Pennsylvanian in age. The sedimentary rock layers dip very gradually to the south and thicken towards the Ouachita Mountains to the south.

The Salem Plateau region extends south of the St. Francis Mountains into northern Arkansas. Sedimentary rocks of marine origin make up the bedrock of the Salem Plateau, consisting mostly of Ordovician-age dolostone, with some limestone and sandstone. The Salem Plateau region ranges from about 800 to 1,400 feet in elevation.

The Springfield Plateau region of rolling hill country that exists where a belt of Mississippian-age limestone (the Boone Formation) crops out across northern Arkansas. The Boone Formation contains nodular chert beds and the limestone is host to karst erosional characteristics, having caves, caverns, and sinkholes. Highest portions of the plateau region reach about 1,800 feet in elevation. The Buffalo National River is a scenic preserve in the region (Figure 61).

The Boston Mountains Plateau region have surficial rocks of Early Pennsylvanian age, composed mostly of sandstones and shales. The highest parts of the erosionally-dissected plateau has elevations in the range of 2,200 to 2,500 feet.

Geologic map of the Ozarks Plateau Province of Missouri, Arkansas, and eastern Oklahoma. Fig. 60. Geologic map of the Ozarks Plateau Province of Missouri, Arkansas, and eastern Oklahoma.
Limestone cliffs along the Buffalo River, a national scenic river, illustrated the character of the incised Ozark Plateau.
Fig. 61. Limestone cliffs along the Buffalo River in Arkansas, a national scenic river, illustrated the character of the incised Ozark Plateau.

Ouachita Orogenic Belt

Ouachita Mountains Province

The Ouachita Mountains are a mountain range that runs generally east to west across southwestern Arkansas into southeastern Oklahoma (Figures 62 and 63). The Ouachita Mountain consist of a belt of folded and thrust-faulted sedimentary rocks ranging in Ordovician to Pennsylvanian age, similar in age and character to the Valley and Ridge region. The Ouachita Mountains are only an small portion of the greater Ouachita Orogenic Belt, a region geologically similar in age and origin of the Southern Appalachians. Most of rocks of the Ouachita Orogenic Belt are covered by younger sediments of the Mississippi Embayment, the Gulf Coastal Plain, and Great Plains regions of Central Texas (see Figure 59).

Current thought is that the Ouachita Orogenic Belt started forming about 300 million years ago (Pennsylvanian time) when the North American and South American continental plates collided as all the continents gradually assembled together to form the supercontinent Pangaea. Sedimentary deposits from an ancestral ocean basin in the Gulf region were thrust northward and upward onto the southern margin of the southern North American continental margin. At one time, the Ouachita Mountains possible rivaled the current elevations of the Rocky Mountains. The ancient mountains shed large quantities of sediments that filled basins and covered lowlands across the Great Plains region. Today, the highest peak in the Ouachita Mountains is Mt. Magazine in Arkansas, elevation 2,753 feet.

Bedrock of the Ouachita Mountains are notably unique in that they do not preserve evidence of igneous intrusions, volcanism, or regional metamorphism. Sedimentary rocks in the Ouachita Mountains range from Cambrian to Pennsylvanian age, mostly marine shales, sandstone, and chert. The region is famous for very hard, fine-grained, siliceous sedimentary rock called novaculite (the State Rock of Arkansas)(Figure 64). Novaculite was used as whetstones for sharpening tools, and was used extensively by prehistoric indians for arrowheads, spear points, and tools.

Arbuckle Mountains (Oklahoma)

The Arbuckle Mountains are ancient mountain range located in south-central Oklahoma. The Arbuckle Mountains also formed about the same time as the Ouachita Orogeny, but along a failed structural rift separate from, and perpendicular to, the orogenic belt (called the Southern Oklahoma Aulacogen). In addition, the Arbuckle are composed of rocks that are both older and different composition. The exposed rocks are composed of granite of Precambrian age (about 1.4 billion years). These are overlain by Cambrian-age volcanic rocks and are flanked by early Paleozoic sedimentary rock formations that were structural deformed uplifted to near vertical orientation. These rocks are, in turn, overlain by younger conglomeratic sediments of Pennsylvanian and Permian age that rest unconformably on the older deformed rocks. The highest peak in the Arbuckle Mountains is 1,412 feet.

Wichita Mountains (Oklahoma)

The Wichita Mountains are another small mountain range located in southwestern Oklahoma (Figure 65). The Wichita Mountains also formed about the same time as the Arbuckle Mountains and along the same east-to-west structural trend. Rocks exposed in the Wichita Mountains consist of 540 million year old granite which were exposed to weathering and erosion in Permian time. The granitic peaks rise as much as 1,000 feet above the surrounding rolling grasslands.
View of the southern Ouchita Mountains from Talamina Ridge Drive, southern Oklahoma
Fig. 62. View of the southern Ouachita Mountains from Talamina Ridge Drive, southern Oklahoma.
Hot Springs (National Park) is on the boundary between the Ouachita Mounains and the Coastal Plain near Little Rock, Arkansas
Fig. 63. Hot Springs National Park is on the boundary between the Ouachita Mountains and the Coastal Plain near Little Rock, Arkansas.
Novaculite , deep, cold water ocean deposits of Orodovican age, also the state rock of Arkansas, is well exposed in Hot Springs National Park, Arkansas
Fig. 64. Novaculite, the state rock of Arkansas, formed from deep, cold water ocean deposits of Ordovician age, Outcrops of it are is well exposed in Hot Springs National Park, AR.

Anadarko Basin (Oklahoma and Texas Panhandle)

The Anadarko Basin is one of the deepest sedimentary basins in North America, about 40,000 feet near its deepest point near Anadarko, Oklahoma (Figure 66). The basin covers about 50,000 square miles in western Oklahoma and part of the Texas Panhandle region. The Anadarko Basin is important in that it is the most productive natural gas production region of the United States. The basin is also a source of petroleum. Production of oil and natural gas occurs both in the basin and along the surrounding flanking margins. The oil and gas field brines are the main commercial source of iodine in the United States. The Anadarko Basin is also the major source of helium (extracted from the natural gas). Current thought is that the helium is derived from the decay of radioactive elements in the ancient granite wash deposits buried along the flank of the Wichita Uplift.

The Anadarko Basin formed in Late Paleozoic time as part of the Southern Oklahoma Aulacogen—the structural basin sank and filled with sediments shed from surrounding rising uplifts in the region, primarily during Pennsylvanian time (concurrent with the Ouachita Orogeny). The deepest part of the basin is adjacent to the Wichita Mountains-Amarillo Uplift on its southern margin. The basin is bounded on northeast by the Nemaha Ridge (a buried uplift), and by the Amarillo Uplift and Cimarron Arch (also buried uplifts) to the west and northwest.

At the time of the writing of this report, Oklahoma, partially parts of the Anadarko Basin, have been experience an abundance of low-to-moderate magnitude earthquakes. The earthquakes have been "attributed" (proving is difficult) to the increased intensity of drilling and fracking taking place in the Anadarko region. Current thought is that the drilling and fracking activity is releasing potential energy associated with old fault systems in the region, currently making Oklahoma the most seismically active region in the United States.

Arbuckle Mountains in southwestern Oklahoma
Fig. 65. Wichita Mountains of southwestern Oklahoma.
North-south cross section of the Anadarko Basin, Oklahoma. Fig. 66. North-south cross section of the Anadarko Basin, Oklahoma.

The Great Plain Province

The Great Plains is the largest province in North America, extending from the Northwest Territory in Canada southward to the Texas-Mexico border, and from the Mississippi River Valley to the Front Ranges of the Rocky Mountains (Figure 67). The Great Plains is a “steppe” region, highlighted as tall-grass prairies and corn-belt agriculture in the east to more arid short-grass prairies and open-range lands to the west. The region is characterized by flat lands to low rolling hill country. The Great Plains have a dry continental climate with abundant sunshine, frequent winds, and moderate precipitation. Average annual precipitation ranges from 33 inches in the east to 12 inches in the west. The eastern side of the plains are transitional to shrub-oak dominated forests. Cottonwood and willow riparian forests dominate river valleys draining eastward across the region from the Rocky Mountains.

A drive westward across the Great Plains illustrates the subtle changing character of the Great Plains. To the east, Missouri River flood plain near Kansas City, Missouri is about 700 feet in elevation. 600 miles to the west, elevations range from 5,000 to 6,000 feet along the Front Range near Denver, Colorado (“Mile High” City). The region is a very gentle incline, shaped by the geologic history of the region.

During the Late Cretaceous time, the entire Great Plains region was covered by the Western Interior Seaway (Figure 68). As the Rocky Mountain began to rise and shed sediments, the shallow seaway gradually transitioned to coastal swamplands and lowland plains. With time, both the Rocky Mountains and western plains region began to rise, and river systems draining from the Rocky Mountains accumulated a great, coalescing series of alluvial fans that eventually spread across the entire region by Miocene time. The ancient alluvial plain deposits are preserved as the Ogallala Formation (Miocene age), the principal groundwater aquifer underlying a large part of the western Great Plains region (Figure x). Since Miocene time, the region has continued to steadily rise, and rivers have began to slowly incise into their valleys, producing a series of low plateaus and escarpments across the region.

The continental glaciers covered a large portion of the northern Great Plains region during the Quaternary Period. In the United States, most of North Dakota, eastern South Dakota, and portions of Montana and Kansas were covered intermittently with ice sheets (see Figure 67). South of the ice sheet were outwash plains which released silt and dust to the wind. Large portions of the Great Plains and Midwestern states were blanketed with loess (glacial dust deposits), and some grew into great dune fields covering large regions that are now covered with prairie grasses (example, the Sand Hills region of western Nebraska).

Great Plains
Fig. 67. Physiographic map of the Great Plains region in the United States.
Map of the extent of the Western Interior Seaway during the Late Cretaceous Period.
Fig. 68. Map of the extent of the Western Interior Seaway during the Late Cretaceous Period (70-90 million years ago).
  Map of the Great Plains Physiographic Province showing the extent of the High Plains Aquifer (Ogallala Formation). Physiographic regions in Texas and the southern Great Plains. Amarillo, Texas, host to Cadallac Ranch (shown here) is one of the flattest landscapes in North America.
  Fig. 69. Map of the Great Plains Province showing the extent of the High Plains Aquifer (Ogallala Formation). Fig. 70. Physiographic regions of southern Great Plains of Texas and New Mexico. Fig. 71. Amarillo, Texas is one of the flattest landscape regions in North America (illustrated here at Cadillac Ranch).

High Plains and Plateaus of West Texas

The High Plains are a sub region of the Great Plains Province that roughly corresponds with the outcrop belt of the Ogallala Formation ranging from western South Dakota south to the Texas Panhandle (Fig. 69). The region ranges in elevation of about 1,200 feet to over 7,800 feet. The southern Great Planis is subdivided into many sub regions, each with their own characteristic features (Figure 70).

Llano Estacado

Amarillo is located on the Llano Estacado is the southern portion of the High Plains in the region south of the Canadian River on the Texas Panhandle. The plains landscape around Amarillo, Texas (elevation 3,606′) is one of the flattest regions in North America (Figure 71). The eastern boundary of the Llano Estacado is the Caprock Escarpment, a prominent rim of cliffs and canyons carved in the headwater regions of tributaries the Red and Brazos Rivers in West Texas (Figure 72). Below a caprock of Ogallala Formation, red rock layers of Permian and Triassic age are exposed along the canyon and escarpment.

Palo Duro Canyon is Often called the “Grand Canyon of Texas” —it is the second largest canyon in the United States (Figure 73). The canyon is located on the Prairie Dog Town Fork of the Red River, about 30 miles south of Amarillo. The canyon about 70 miles long and between 6 and 20 miles wide, and 800-1,000 feet deep. The canyon is incised into the surface of the Llano Estacado and cuts through the Caprock Escarpment.

The Llano Estacado extends west to the Mescalero Escarpment that faces the eastern foothills of the Southern Rocky Mountains, Sandia Mountains, and Sacramento Mountains of New Mexico.

Edwards Plateau

The Llano Estacado gradually transitions into the Edwards Plateau to the south and east in central Texas (see Figure 70). The eastern end of the Edwards Plateau is called Texas Hill Country—a region characterized by forested high hills with bedrock of karst limestone and granite, and valleys with broad floodplains. Texas Hill Country is bound on the north by the Llano Uplift (Figure 74). The southeast side of the Edwards plateau is bordered by the Balcones Escarpment, a line of hills associated with the Balcones Fault Zone. The Texas cities of Austin and San Antonio are spread along the Balcones Escarpment.
Caprock Canyons State Park, Texas is part of the eastern escarpment of the Edwards Plateau in West Texas.
Fig. 72
. Caprock Canyons State Park, Texas is part of the eastern escarpment of the Llano Estacado in West Texas.
Palo Duro Canyon near Amarillo, Texas
Fig. 73
. Palo Duro Canyon, located 30 miles south of Amarillo, is called "The Grand Canyon of Texas."
 

Ouachita Orogenic Features in Texas

The rise of the Rocky Mountains shed sediments that blanketed the entire region gradually, filling in valleys and burying older regional upland landscape features through most of Cenozoic time. Late Tertiary regional uplift and climate changes during the Pleistocene ice ages has allowed erosion to re-expose some of the older geologic structures in the region, including the Llano Uplift and the Marathon Mountains.

The Llano Uplift is located in central Texas region in the northern part of the Texas Hill Country and east of the Edwards Plateau region. It is a roughly circular dome of g exposed crystalline basement rocks of Precambrian-age. Bedrock at the center of the uplift consists granite, such as those exposed in Enchanted Rock State Park, Texas (Figure 74). The granite surrounded by a belt of metamorphic rocks (chiefly gneiss and schist) with an outer margin along the flanks that consist of limestone of Early Paleozoic age that locally forms low escarpments and ridges. The Llano Uplift is another geologic structure that formed concurrent with the Ouachita Orogeny, although it is not part of the thrust-faulted orogenic belt that is buried beneath the sedimentary cover further south.

The Marathon Mountains of West Texas are the western-most exposure of rocks associated with the Ouachita Orogenic belt. This mountainous area covers a region about 80 miles in diameter (Figure 75). Rocks exposed along the flanks of the uplift include folded sedimentary layers of Early Paleozoic (pre-Permian) age. The Paleozoic-age strata exposed includes novaculite that are exposed in northeast-trending ridges (consistent with general trend of the Ouachita Orogenic Belt; see Figures 59, 70, and 76). An angular unconformity separates these folded layers from overlying flat-lying marine sedimentary rocks of Cretaceous age. Regional uplift and erosion during the Cenozoic Era have exposed the older rock formations on the flanks of the low mountain range. The mountains are a geologic dome-like feature that rise about 800 feet above lowlands in the surrounding region.

Enchanted Rock, a large outcrop of granite exposed in the core of the Llano Uplift. Fig. 74. Enchanted Rock, a large outcrop of granite exposed in the core of the Llano Uplift.
Layers of novaculate and sandstone form serrated hogback ridge lanogh the flank of the Marathon Uplift.
Fig. 75. Layers of novaculite and sandstone of Paleozoic age form a serrated hogback ridge along the flank of the Marathon Uplift.

Permian Basin (West Texas and New Mexico)

The Permian Basin is one of the largest sedimentary-filled basins in North America, located in West Texas and southeastern New Mexico (Figure 76). The Permian Basin is actually three interconnected basins, the Delaware, Midland, and Val Verde basins—separated by a central basin platform (a structural high in the middle of the larger basin). At the time the basin formed and filled, concurrent with the development of the Ouachita Orogenic Belt, the Permian Basin was a restricted seawater-filled foreland basin. The margins of the basins had shallow shelves where small to great organic reef tracks built up (such as the great Guadalupe Reef exposed in Guadalupe Mountains National Park). The Permian Basin had a link to the open ocean that allowed seawater to flow in. High evaporation rates, combined with the restricting geometry of the basin, allowed great quantities of salt to gradually fill the basins. The deepest parts of the sedimentary basin are in excess of 25,000 feet.

The Permian Basin has been one of the most prolific oil and gas-production regions in North America. Oil drilling and production in the region began in the 1920s, targeting petroleum reservoirs in buried reefs, reef flank deposits, and reservoirs on the basin’s central platform and shelf margins, and estimates of as much as 40 billion barrels of oil and liquefied natural gas have been extracted from the basin by the end of the 20th century. It is now considered a “mature” basin, with secondary oil recovery methods being used to prolong the life of old oil fields.

The basin is filled with great deposits of salt and anhydrite. Mining of gypsum, salt, and sylvite (potassium-chloride salt, also called “potash”) is also a large industry in the region. The salt deposits are part of the massive and extensive Castille Formation of Permian age.

The massive Permian-age reefs exposed in the Guadalupe Mountains are integral to the scenery in Guadalupe Mountains National Park, Texas (Figure 77). The same reef track is host to Carlsbad Cavern National Park in the Guadalupe Mountains in southeast New Mexico (Figure 78). Carlsbad Caverns has been developed as a public-accessible "show caves" and is part of one of the largest cavern systems in North America.

Map of the Permian Basin region of West Texas and New Mexico
Fig. 76. Exposed and buried reefs and structures in the Permian Basin region, West Texas and New Mexico.
Guadelupe Peak, the highest point in Texas, is an exposed part of the great fossil Permian Reef system.
Fig. 77. Guadalupe Peak, the highest point in Texas, is an exposed part of the great fossil Permian Reef system.

High Plains of Eastern New Mexico

The High Plains region on the western side of the Edwards Plateau (west of the Mescalero Escarpment) is a piedmont region of Southern Rocky Mountains (see Figure 76). It is rolling prairie country with scattered oak-forest covered hills and grasslands with many playas (dry lake beds). During wet periods the playas are flooded, but dry out during drought periods. The High Plains region experiences occasional strong winter snowstorms, summer thunderstorms and intense wind events, the source of large dust clouds that move eastward across the southern Great Plains region.

The High Plains of eastern New Mexico are also transitional to the general geology of the Basin and Range Physiographic Province (characterized by extensional faulting and rift volcanism). The Sacramento Mountains border the Rio Grande Rift Valley, a great structural graben that marks the eastern margin of the Basin and Range Province. In northeastern New Mexico is the geologically "young" Raton-Clayton Volcanic Field started forming about 9 million years ago, with the last eruption having occurred about 50,000 years ago (Figure 79).
Carlsbad Caverns, one of the largest caverns in the world, formed in the great Permian Reef Complex in southern New Mexico. The Raton-Clayton Volcanic Field near Capulin Volcano National Monument, northeastern New Mexico.
Fig. 78. View of massive stalagmites in Carlsbad Caverns NP's Big Room. The cavern is part of a large karst/cavern system formed in the great Permian Reef Complex in southern New Mexico. Fig. 79. The Raton-Clayton Volcanic Field located in northeastern New Mexico, includes a young cinder cone, featured in Capulin Volcano National Monument.

Central Great Plains

In the High Plains regions (northern Texas to Nebraska) roughly corresponds to the outcrop belt of the Ogallala Formation, and a piedmont region on the east side of the Rocky Mountains (Figure 80). The Ogallala Formation overlies and rests unconformably on an eroded surface of rocks of Permian to Cretaceous age. The Ogallala Formation is composed of alluvial plain sediments that were deposited in stages in Miocene through Pliocene time. Rivers crossing the region are now downcutting through this alluvial plain, producing several step-like terraces visible along river valleys in the region.

The Antelope Hills are a National Registered Landmark located in along a series of bends in the Canadian River on the Oklahoma Panhandle (Figure 81). They are a series of low erosional buttes that rise about 200 feet above the surrounding plain and consist of eroded remnants of the upper Ogallala Formation.The highest peak is 2,585 ft. The buttes were a major landmark used by the Plains Indians, Spanish explorers, and early settlers on route to California.

Physiographic regions in the north-central Norther Great Plains, Kansas, Nebraska, Eastern Colorado, and southern South Dakota.  Antelope Hills in the Ohlahoma Panhandle.
Fig. 80. Physiographic regions in the central and northern Great Plains of Oklahoma, Kansas, Nebraska, Eastern Colorado, and southern South Dakota. Fig. 81. Antelope Hills in the Oklahoma Panhandle are an erosional remnant of the upper Ogallala Formation of Pliocene age.

Great Plains of Kansas to Eastern Colorado

For many folks, the drive across the Great Plains on Interstate 70 (From Kansas, City, Missouri to eastern Colorado) seems "remarkably unremarkable." The east side of Kansas is partially forested rolling hill country of the Osage Plains (or "Osage Cuestas") near the Missouri River to open prairie (now mostly croplands for corn, soybeans, etc.) near Topeka. West of Topeka, the Flint Hills of eastern central Kansas is a region of low hills and escarpments of Permian-age limestone and siliceous chert (or flint)(Figure 82). Settlers found that the thin soils and cherty gravel on top of the rocky escarpments make the region less-than idea for farming, and better suited for cattle range. The highest elevation in the Flint Hills is 1,680 feet.

West of the Flint hills the Great Plains landscape grows increasing flat and drier. The corn-soybean agriculture transitions to range land and dry-land farming of wheat and other grains, and sunflowers (the State Flower of Kansas). In the region between Salina and Hays, Kansas, I-70 crosses a region of low rolling hills and escarpments. The Smoky Hills, Blue Hills, and Chalky Buttes each correspond to belts of Cretaceous age rock formations (originally deposited in the Western Interior Seaway)(Figure 83). Monument Rocks National Natural Landmark is an exposure of the Cretaceous-age chalk beds capped by Ogallala Formation (Figure 84). Traveling west from Salina, Kansas the landscape slowly rises—elevations: Salina (1,227 feet), Hays (2,021), Goodland (3,681 feet), and Limon, Colorado (5,377 feet). Between Limon, Colorado and the Front Range of the Rocky Mountains is the Colorado Piedmont, a region characterized by rolling grasslands, patchy pine forests, and cottonwood groves along stream valleys east of the Rocky Mountains (Figure 85).

  The Flint Hills of eastern Kansas is characterized by low escarpments and thin, cherty gravel soils. Smoky Hills windfarm. Monument Rocks National Natural Landmark, central Kansas Rolling hill country around Limon, Colorado with the Colorado Front Range in the distance.
  Fig. 82. The Flint Hills of eastern Kansas is characterized by low escarpments and ridges covered with thin, cherty gravel soils. Fig. 83. A wind farm in the Smoky Hills region of central Kansas. Large wind turbine fields are a fast growing industry on the Great Plains. Fig. 84. Monument Rocks National Natural Landmark, western Kansas, are eroding remnants of Cretaceous chalk capped with Ogallala Formation. Fig. 85. Rolling hill country of the Colorado Piedmont near Limon, Colorado provides a view of the Colorado Front Range in the distance.

Great Plains of Nebraska and Southeastern Wyoming

The drive west across Nebraska on Interstate 80 is perhaps even more "remarkably unremarkable" than the drive of I-70 across Kansas. The eastern part of Nebraska is mostly crop farming (corn, soybeans, etc), the western part of the state is mostly rangeland and dry-land farming (wheat and other grains). The region east of the Missouri River is glaciated terrane— rolling plains and low hills underlain by glacial till and loess deposits (loess is fine-silty dust eroded from barren lands and outwash plains south of the continental glaciers)(see Figure 80). Central and northern Nebraska is blanked with loess deposits. The Loess Plains grade westward into the Sand Hills region which, at the end of the last ice age was a dune field. The dunes of Sand Hills are currently stabilized by a fragile cover of grasses (Figure 86).

The elevation of the Great Plains along Interstate 80 steadily rises to the west across Kansas into eastern Wyoming—Omaha (1,089 feet), Lincoln (,1176 feet), Grand Island (1,860 feet), North Platte (2,802 feet), Ogallala (3,222 feet), Kimball (4,715 feet), and Laramie, Wyoming (6,063 feet). West of Kimball, Nebraska is a landscape feature called the "Gang Plank." The Gang Plank is an un-eroded portion of the Ogallala Formation that laps up onto the crest of the granite core of the Laramie Mountains in eastern Wyoming. The gentle grade of the Gang Plank allowed for only easy passage for the Transcontinental Railroad over the front range of the Rocky Mountains. Interstate 80 also crosses along the Gang Plank.

The northwestern portion of Nebraska is characterized by mesas, bluffs, and buttes eroded into older sedimentary rock formations of the White River Group (ages Eocene to Miocene). These formations are composed of alluvial plain deposit that blanketed the region after the rise of the Black Hills in South Dakota and mountain ranges farther west in Wyoming. Chimney Rock is a important landmark used by pioneer travelers along the Oregon Trail—it is part of Scotts Bluff National Monument (Figures 87 and 87). Bone beds preserved in layers of the White River Groups are also exposed in Agate Fossil Beds National Monument in northwestern Nebraska (Figure 89).
San Hills of Nebraska are stabilized dunes in the northwestern Nebraska prairie. Chimney Rock, Nebraska is a prominent landmark on the Oregon Trail in Western Nebraska. Scotts Bluff was a stopping point on the Oregon Trail. Agate Fossil Beds National Monument preserves fossiliferous outcrops of the White River Formation exposed in northwestern Nebraska.
Fig. 86. Sand Hills of Nebraska are a large, stabilized dune field covered by grasses. The Sand Hills cover large parts the northwestern Nebraska into South Dakota. Fig. 87. Chimney Rock is a historic natural landmark along the Oregon Trail in Western Nebraska; it consists of Oligocene and Miocene-age sedimentary rocks. Fig. 88. Beds of the White River Group (Oligocene) and Arikareee Formation (Miocene) crop out at Scotts Bluff National Monument, northwest Nebraska. Fig. 89. Agate Fossil Beds National Monument preserves fossiliferous outcrops of the White River Formation exposed in northwestern Nebraska.

Northern Great Plains

The Northern Great Plains include North and South Dakota, and eastern Montana and Wyoming (Figure 90). Most of the eastern and northern portions of the region experienced glaciation, and the landscape consists mostly of low rolling hill country typical of surficial glacial moraine and till deposits. Interstate 90 crosses southern South Dakota into Northern Wyoming. Between Sioux City and Chamberlain, I-90 cuts through croplands on the glaciated till plain. Chamberlain, SD overlooks the "Breaks of the Missouri"—the incised canyon of the Missouri River. Landslide-prone slopes exposed the Pierre Shale of Late Cretaceous age (Figure 91). The Pierre Shale underlies most of South Dakota and represents sediments deposited in the Late Cretaceous Seaway. The elevation of the Missouri River crossing at Chamberlain is 1,354 feet. To the west of Chamberlain, the land steadily rises to Wall, SD (2,825 feet). South of Wall is Badlands National Park, famous for its fossiliferous exposures of the White River Group—a group of rock formations that range in age from Eocene to Miocene age (Figure 92). The White River Group preserve evidence of the character of the after the withdrawal of the Western Interior Seaway—coastal lowlands, to upland forests, to high western desert prairie climates. The name "badlands" refers to the impression of the eroding landscape held by early settlers heading west. Badlands National Park was also established as a preserve for American Bison (commonly called buffalo) that were nearly wiped to extinction in the late 19th century (Figure 93).
Northern Great Plains - South Dakota, North Dakota, eastern Montana and Wyoming. Breaks of the Missouri, hill country along the Missouri River in Chamberlain, South Dakota. Badlands National Park, South Dakota Bison on prairie in Badlands National Park, South Dakota
Fig. 90. Northern Great Plains - South Dakota, North Dakota, eastern Montana and Wyoming. Fig. 91. Breaks of the Missouri, hill country along the Missouri River in Chamberlain, South Dakota. Fig. 92. Tertiary sedimentary rocks of the White River Group erode into badlands in Badlands National Park, South Dakota. Fig. 93. American Bison in grazing on short-grass prairie in Badlands National Park, South Dakota.

The Black Hills

West of Wall, South Dakota, Interstate 90 descends through the Breaks of the Cheyenne River where Pierre Shale is also well exposed. At Rapid City, SD (elevation 3,202 feet), I-90 skirts around the north side of the Black Hills Uplift before it crosses into the high rolling plains of the Powder River Basin of eastern Wyoming. The Black Hills are an outlier of the Rocky Mountains, a massive mountainous dome that rose above the Western Interior Seaway starting about 70 million years ago (Figure 94). Over millions of years, erosion has stripped away thousands of feet of sediments, exposing ancient rocks in the core of the Black Hills. The core's bedrock is composed of both metamorphic and plutonic igneous rocks ranging 1-8 to 2.8 2 billion years. Harney Peak (elevation 7,244) is the highest peak in the Black Hills, it is composed of Precambrian-age granite (Figure 95). Mount Rushmore National Monument is carved into the granitic core rocks (Figure 96).

The sedimentary rock formations of Paleozoic and Mesozoic age crop out on the flanks of the uplifted core. Large cavern systems have formed in the rising Black Hills Uplift including those in Wind Cave National Park, Jewel Cave National Monument, and many others occur in Mississippian-age marine limestones in the outcrop belt around the core. During the Triassic and Jurassic Periods, the Black Hills region was lowlands that occasionally was flooded by shallow seas. Paleozoic rocks are overlain by Triassic red-beds, Jurassic layers consist of limestone, sandstone and shale. Lowlands surrounding the black hills consist of Late Cretaceous marine shales deposited in the Western Interior Seaway. Laramide Orogeny is the name of the mountain-building period when the large ranges in the Wyoming and Colorado Rocky Mountain ranges were uplifted. Initially shallow inland seas flooded the basin between rising mountain ranges. Over time, the rising Laramide mountain ranges flooded the surrounding regions, filling the basins with sediments. In the Powder River Basin and around the Black Hills these sediments are preserved as the White River Group (Eocene to Miocene time), best known for exposures in Badlands National Park.

Laramide volcanism: Scattered around the northern Black Hills are a about a dozen igneous intrusion structures that formed in early Tertiary time during the peak of the Laramide Orogeny. Devils Tower National Monument is named for the famous natural landmark in northeastern Wyoming (Figure 97). Devils Tower is the eroded remnant of what may have been a laccolith (an intrusive body trapped between sedimentary layers) or possibly the stock of a volcano (however, any trace of a what many have been volcano have eroded away).
Geologic map of the Black Hills region, South Dakota and Wyoming. Harney Peak, the highest peak in the Black Hills, South Dakota. Mount Rushmore National Monument, South Dakota Devils Tower, Wyoming.
Fig. 94. Geologic map of the Black Hills region, South Dakota and Wyoming. Fig. 95. Harney Peak, the high point in granitic core of the Black Hills of South Dakota. Fig. 96. Mount Rushmore National Monument in the Black Hills of South Dakota. Fig. 97. Devils Tower NM, Wyoming is the erosional remnant of a volcanic stock.

Great Plains of North Dakota and Eastern Montana

Interstate 94 crosses the Northern Great Plains between Fargo North Dakota to Billings, Montana, (see Figure 90). East of Fargo, the landscape is is covered with forests and many small lakes. West of Fargo, the forest transitions to prairie grasslands and agricultural croplands. Between Fargo and Bismarck, North Dakota, the interstate crosses glaciated-till plains. West of Bismarck (on the Missouri River), the climate grows dryer and crop farming transitions to range land and dry-land farming. Along the western side of North Dakota, the Little Missouri River has carved a canyon with badlands exposing sediments of the Cannonball Formation of Paleocene age. Theodore Roosevelt National Park is a American Bison preserve in the heart of the Little Missouri River badlands region (Figure 98).

The Paleocene-age Cannonball Formation was deposited in the Cannonball Sea, a remnant of the once greater Western Interior Seaway. The outcrop belt of the Cannonball Formation roughly outlines the extent of the Williston Basin, a large structural basin that approaches 12,000 feet thick at its center (Figure 99). The Williston Basin began to form in middle Paleozoic time. Late Paleozoic-age formations grow increasing thicker toward the center of the Basin. The Williston Basin is currently experiencing a oil and gas drilling boom utilizing fracking technologies.

The region around Miles, Montana is famous for dinosaur hunting. The Hell Creek Formation of Late Cretaceous age was deposited on the coastal plain of the Western Interior Seaway. Fossils of dinosaurs Tyrannosaurus rex, Triceratops, and many others have been mined from this region (Figure 100).

The Montana city of Great Falls takes its name from a series of 5 waterfalls along the upper Missouri River. It is famous for the arduous task of portage around the falls by the Lewis and Clark expedition (1805-6)(Figure 101).
Theodore Roosevelt National Park encompasses the Little Missouri River in the Williston Basin region of North Dakota. Cross sections of the Williston and Powder River Basins, Montana, North  and South Dakota, and Wyoming
Fig. 98. Theodore Roosevelt National Park encompasses the Little Missouri River in the Williston Basin region of North Dakota. Fig. 99. Geologic cross sections of the Williston Basin (Montana and North Dakota), and the Bighorn Basin (northeast Wyoming).
Hell Creek badlands near Miles, Montana. Great Falls on the Missouri River in Montana.
Fig. 100. Hell Creek badlands near Miles, Montana is a target of many dinosaur-hunting expeditions. Fig. 101. Great Falls on the Missouri River in Montana is famous for the famous portage of the Lewis and Clark Expedition.

North American Cordillera

The entire region west of the Great Plains is collective lumped together and are called the Cordilleran Ranges, part of the great chain of mountains that border the Pacific Ocean from Alaska to South America. The North American Cordillera is subdivided into the Eastern Cordilleran Ranges (which include the Rocky Mountains) and the Western Cordilleran Ranges (which include the Coast Ranges, Cascades, and Sierra Nevada)(see Figure 1).

Evolution of Western North America

The following brief synopsis of the the geologic evolution of the western half of North America is perhaps the best way to start an examination of the physiographic regions of the western United States (Figure 102).

At depth, ancient crystalline basement rocks of Precambrian age underlie most of the United States. Crust that had assembled into the stable cratonic shield in Precambrian became foreland basins where sediments accumulated across much of Midwest and Great Plains. At the same time, sediments spread accumulated in the Pacific Ocean margin basin (Figure 102A). In the early Paleozoic Era, shallow seas transgressed and retreated several times onto the stable continental foreland. Thick packages of sedimentary rock, mostly marine limestones, accumulated across much of what is now the western United States.

By Mid Paleozoic time the western foreland margin began to undergo tectonic changes with a mountain-building event called the Antler Orogeny (Figure 102B). The Antler orogeny impacted the impacted the continental margin region beginning in Late Devonian and continuing into early Pennsylvanian time. The orogeny impacted what is now the Nevada region, but the effects may have been more widespread.

By Pennsylvanian time, tectonism impacted the foreland region, producing the ancestral Rocky Mountains (Figure 102C). Along the West Coast, sediments continued to accumulate along the continental margin and shallow warm seas flooded onto the continental platform. Small island arcs formed along westward-dipping subduction zones. some of these small island arcs were eventually ripped apart and accreted as terranes onto the Pacific continental margin.

The breakup of supercontinent Pangaea in Mesozoic time changed western North America from a passive to an active continental margin. Subduction changed from west-dipping to east-dipping, and volcanic arcs began forming along greater Cordilleran mountain belt)( Figure 102D). The Nevadan Orogeny in Mid- to Late-Jurassic time (180 to 140 million years ago) resulted in the formation of the Cordilleran volcanic arc which included the ancestral Sierra Nevada and Peninsula Ranges of California.

Over time the Nevadan Orogeny transitioned into the Sevier Orogeny, a mountain-building period that affected the entire Cordilleran region (Canada to Mexico), lasting from 140 million to 50 million years ago. The orogeny was produced by the subduction of the Farallon Plate beneath North America. Tectonic compression and sub-crustal heating pushed up thrust-faulted mountain belts in what was previously the foreland shelf and continental margin basin regions (western Utah and Wyoming regions). The weight of the ranges and the sediments they contributed worked to push down the mid continent region, allowing the Western Interior Seaway to flood across the continent (Figure 120E, see also Figure 68).

The mountain building continued to migrate eastward during the Laramide Orogeny. The Laramide Orogeny occurred in a series of pulses of uplift and volcanism that impacted the greater Rocky Mountain Region between about 80 million to 35 million years ago (Figure 102F). Laramide mountain building overlapped the Sevier mountain building further west. Current thought is that North America overrode the Farallon Plate at a rapid pace and a low angle, disrupting subduction or moving it further east. Sediments from Laramide ranges gradually filled in the Western Interior Seaway basin.

In late Cenozoic time, North America began to override the spreading center that formed the boundary between the Farallon Plate and the Pacific Plate (Figure 102G). As the spreading center as moved eastward under North America, crustal compression changed to crustal extension, resulting in the opening of formation of the Great Basin and Basin and Range structural regions. Sub-crustal heating resulted in the regional rise of the entire region including the Rocky Mountains, Colorado Plateau, and western Great Plains.
Geologic evolution of the western United States region
Fig. 102. Generalized geologic evolution of western United States from Late Precambrian time (1 billion years) to the present.
Types of mountains found in the Central Rocky Mountains
Fig. 103. General types of mountains found in the western United States included tectonic mountains (folds, faults), erosional mountains, volcanic mountains, and complex combinations of all kinds.

Rocky Mountains Provinces

The Rocky Mountains are subdivided into three provinces: The Northern Rocky Mountains (Montana and western Canada), Wyoming Ranges and Basins (or Central Rockies), and the Southern Rocky Mountains (Colorado and New Mexico). Starting in Miocene time, the entire Western Great Plains and Rocky Mountain regions have gradually rose about a mile above sea level.

Southern Rocky Mountains

The Southern Rocky Mountains include ranges in Colorado and New Mexico (Figure 104). Colorado alone has 53 mountain peaks over 14,000 feet in elevation, but none taller than Mt. Elbert in the Sawatch Range (elevation 14,440 feet). These mountains rise from their valleys and foothills with elevations between 5,000 to 8,000 feet.

The Southern Rocky Mountains have a long history, starting with the uplift of the ancestral Rocky Mountains in Pennsylvanian time when much of North America was experience tectonic upheavals and mountain-building as the North American Plate collided with South America, Africa, and Eurasia to form the supercontinent Pangaea. During Pennsylvanian time, uplift an erosion scoured away the older sedimentary cover, exposing crystalline basement rocks. Sediments eroded from these ancient mountains are preserved along the flanks of the modern mountain ranges as the Fountain Formation, a conglomeratic "arkose" alluvial deposit of Pennsylvanian age (Figures 105 to 107). The ancestral Rocky Mountains gradually wore away. By Mesozoic time, the region was a low coastal plain (home to dinosaurs preserved in the Jurassic Morrison Formation). The region was likely submerged by marine waters of the Western Interior Seaway in Cretaceous time.

The Laramide Orogeny started impacting the Southern Rocky Mountain region in Late Cretaceous time, and the Western Interior Seaway retreated as the first phase of mountain building began to push up the modern Rocky Mountains. The modern Rockies roughly formed in the same regions of the Ancestral Rockies, probably reactivating many of the faults in the region. Near the end of the Laramide Orogeny the Southern Rocky Mountains experienced scattered volcanism including in parts of the Front Range and the San Juan Mountains regions. Uplift proceeded in stages through early Tertiary time, and then the entire region started to rise again starting in Miocene time, lifting the entire Rocky Mountains and western Great Plains nearly a mile.

Nearly all of the high mountain areas where host to alpine glaciers during the Pleistocene ice ages. Alpine glaciers carved U-shaped valleys and tarn (glacial lakes with moraine dams). The Rocky Mountains still has a few small glaciers and ice fields in the high country in the Colorado Front Range, such as in Rocky Mountain National Park (Figure 108). Great Sand Dunes National Park is a massive dune field that has accumulated along the western flank of the Sangre de Christo Mountains in the San Luis Valley (Figure 109).
Southern Rocky Mountains region of Colorado and New Mexico.
Fig. 104. Southern Rocky Mountains region of Colorado and New Mexico.
Fountain Formation exposed at Red Rocks Ampitheatre, Denver, Colorado. Fig. 105. Fountain Formation exposed at Red Rocks Amphitheater, Denver, Colorado.
Fanglomerate of the Permian Fountain Formation Pennsylvanian Fountain Formation in Garden of the Gods, Pikes Peak in the distance, Colorado. Indian Peaks Wilderness, the continental divide in the Colorado Rocky Mountains, Colorado. Great Sand Dunes National Monument on the west side of the Sangre de Christo Range in Southern Colorado.
Fig. 106. The Flatirons of Boulder, Colorado consist of red arkosic conglomerate of the Fountain Formation of Pennsylvanian age. Fig. 107. Pennsylvanian Fountain Formation is exposed in the Garden of the Gods National Natural Landmark; Pikes Peak in the distance. Fig. 108. Indian Peaks Wilderness preserves alpine country along the continental divide in the granitic core of the Colorado Front Range. Fig. 109. Great Sand Dunes National Park preserves a massive dune field on the west side of the Sangre de Christo Range in Southern Colorado.

Central Rocky Mountains and Wyoming Basins

The Central Rocky Mountains include mountain ranges within and bordering Wyoming (Figure 110). The regions between mountain ranges are sedimentary basins that filled to overflowing during erosion periods of the Laramide Orogeny. Precambrian-age crystalline basement rocks (gneiss, schist, and granitic plutonic rocks) are exposed in the core of most of the ranges. Sedimentary rock formations of Paleozoic and Mesozoic age crop out on the flanks of the mountain ranges, including sedimentary beds deposited in the Western Interior Seaway. Brackish water lakes filled basin areas as the mountains were rising in Late Cretaceous to mid-Tertiary time (about 80 to 35 million years ago). The sedimentary basins are quite deep. Deformation during the Laramide Orogeny resulted in displacements in the range of 30,000-35,000 feet along fold and faults systems bordering uplifts in the Wyoming mountain ranges including the Wind River Mountains, Owl Creek Mountains, Bighorn Mountains, and others (Figure 111). For example, the rugged eastern face of Tetons Range in Grand Tetons National Park is an active normal fault scarp with nearly 35,000 feet of vertical displacement (most of the displacement is in the subsurface beneath Jackson Hole, the sediment-filled basin on the east side of the Tetons (Figure 110).

Despite the great amount of uplift, the elevations of the lakes that existed in the basins were still low, as illustrated by palm leaf fossils and other warm-climate species found in lake bed sediments of the Green River Basin (preserved in Fossil Butte National Monument near Kemmerer, Wyoming). Late in the Laramide Orogeny, volcanism resulted in the formation of the Absaroka Mountains about 35 million years ago.

Although Laramide deformation ended in mid-Tertiary time, erosion continued, filling the sedimentary basins and burying mountain ranges in their own sediments. Starting in late Tertiary time (Middle Miocene, about 20 million years ago), the entire region began to rise and erosion began to strip away sediments covering structures in the region. The region has risen more than a mile.
The region is being impacted by sub-crustal heat that is inflating the lower crust with molten material at depth.

Many of the rivers in Wyoming are antecedent streams—an antecedent stream is a stream that maintains its original course and erosional patterns despite the changes in underlying rock topography as the landscape is worn away. Rivers like the Wind River originally flowed eastward across a broad alluvial plain, but erosion over time has allowed to carve its canyon through the Owl Creek Mountains that were completely buried in sediments in mid-Tertiary time. Figures 112 to 119 illustrate landscape features of the central Wyoming ranges and basins.

Wyoming mountain ranges, uplifts, and basins.
Fig. 110. Wyoming mountain ranges, uplifts, and sediment-filled basins. Lowland basins between are similar in character to the High Plains region.
Cross section of the Wind River Mountains and Wind River Basin, Wyoming
Fig. 111
. Cross section through the Wind River Mountains, Wind River Basin, Washakie-Owl Creek, and Absaroka Ranges in northwest Wyoming.
The Grand Tetons are a great block faulted mountain range in northwestern Wyoming. Torrey Canyon is in the glaciated core of the Wind River Mountains, Wyoming, exposing rocks almost 3 billion years old. View of the northwest end of the Absaroka Mountains in the north, Wyoming. Redbeds of the Triassic Chugwater Formation on the northern flank of the Wind River Mountains near Lander, Wyoming.
Fig. 112. The Grand Tetons NP are a great block-faulted mountain range, adjacent to Jackson Hole (a basin) in northwestern Wyoming. Fig. 113. Torrey Canyon is in the glaciated core of the Wind River Mountains, Wyoming, exposing rocks almost 3 billion years old. Fig. 114. View of the northwest end of the Wind River Basin with the volcanic Absaroka Mountains to the north, Wyoming. Fig. 115. Red beds of the Triassic Chugwater Group exposed on the northern flank of the Wind River Mountains near Lander, Wyoming.
Wind River Canyon cuts through the Owl Creek Mountains in central Wyoming. Tensleep Canyon cuts through Paleozoic strata on the west flank of the Bighorn Mountains, Wyoming. Folded layers of Paleozoic and Mesozoic strata crop out along the southern Bighorn Mountains, Wyoming. Granite Mountains in central Wyoming.
Fig. 116. Wind River Canyon cuts through Precambrian rocks exposed in the core of the Owl Creek Mountains Wyoming. Fig. 117. Tensleep Canyon cuts through Paleozoic strata on the west flank of the Bighorn Mountains, Wyoming. Fig. 118. Folded layers of Paleozoic and Mesozoic strata crop out along the southern Bighorn Mountains, Wyoming. Fig. 119. Granite Mountains in central Wyoming formed in Late Cretaceous time, but are being re-exposed by erosion.

Northern Rocky Mountains

The Northern Rocky Mountains include ranges in western Montana (north of Yellowstone National Park) and extending northward into Alberta, Canada (Figure 120). The region was impacted by both the Sevier and Laramide Orogenies. The Lewis Mountains in northern Montana started forming about 140 million years ago as a great slab of sedimentary rocks of Precambrian age (about 3 miles thick) was thrust eastward over rocks of Cretaceous age. Alpine glaciers during the Pleistocene Epoch have carved the Northern Rocky Mountains, resulting in the spectacular scenery of Glacier National Park (Figure 121).

Mountain ranges in southwestern Montana are still actively forming in association with both the Yellowstone Hotspot activity and crustal extension associated with the basin-and-range tectonism of Great Basin Province to the southwest in southern Idaho.
Northern Rocky Mountains Glacier National Park, Montana.
Fig. 120. Northern Rocky Mountains region in Montana and Idaho. The Northern Rockies extend northward into Alberta and British Columbia. Fig. 121. Pleistocene glaciers carved Precambrian sedimentary rocks, now well exposed in Glacier National Park, Montana.

Columbia Plateaus, the Snake River Plain, and the Yellowstone Hotspot

The Columbia River Plateaus region is located west of the Rocky Mountain and east of the Cascades and Coastal Ranges in the Pacific Northwest (Figure 122). The region has unusually catastrophic geologic history. Between 16 and 6 million years ago, massive eruptions of basaltic lava poured from rift zones and flooded the landscape throughout much of central and eastern Washington and Oregon. Floods of lava filled in valleys and eventually covered upland areas over thousands of square miles eventually creating an elevated plain (the Columbia Plateaus). They are collectively called the Columbia River Basalt Group—because they well exposed along the Columbia River Gorge (between Washington and Oregon, Figure 123). South of the Columbia River the region underlain by basalt flows is called the Oregon Plateau (exceptional exposures can be seen at John Day Fossil Beds National Monument, Figure 124). Exposures of the Columbia River Basalt can be seen all along the Columbia River in central and western Washington on the Columbia Plateau.

Grand Coulee, the Spokane Flood, and the Channeled Scablands

Exceptional exposures of the Columbia River Basalt can also be seen along the Grand Coulee—an unusual and scenic gorge with a series of lakes connected only by a small stream. Dry Falls on the Grand Coulee are the remnants of a series of waterfalls and plunge pools that formed from the Spokane Flood, a great flood that occurred at the end of the Pleistocene Epoch when the moraine dam of a huge lake collapsed (Figures 125 to 127). The flood occurred sometime between 18,000 and 12,000 years ago. The lake that existed in northern Washington and parts of Canada was comparable in size and volume to some of the modern Great Lakes. The natural dam probably consisted of loosely consolidated glacial till (rock and soil) that originally accumulated along the advancing front of a great piedmont glacier. The lake possibly drained in a matter of days or weeks, causing flood waters to spread across the relatively flat Columbia River Plateau before finding passage to the Columbia River. Erosion along hundreds of channels formed the Channeled Scablands - a region crisscrossed by dry channels that are generally barren of soil and still preserve many small pools and basins where the floodwaters carved potholes in the channel beds. The Spokane Flood would have dwarfed any known flood in modern history.
Map of the Columbia River Plateau and the Snake River Plain, Oregon, Washington, and Idaho.
Fig. 122. Map showing the extent of the Columbia River Plateaus and Snake River Plain. Both are regions that have experienced massive volcanic rift eruptions that covered the landscape with basalt lava flows.
Columbia River Gorge, Oregon and Washington
Fig. 123. The Columbia River Basalt Group is exposed along the Columbia River Gorge, Oregon and Washington.
John Day Fossil Beds National Monument, Oregon. Sun River Lakes, Washington Dry Falls is where scouring floods that created the Channeled Scablands poured into the Grand Coulee, Washington. floods that Grand Coulee Dam on the Columbia River in central Washington.
Fig. 124. Columbia River Basalt layers exposed in John Day Fossil Beds National Monument, Oregon. Fig. 125. Grand Coulee in the Sun River Lakes area, central Washington, was carved by a great glacial-breakout flood. Fig. 126. Dry Falls is where scouring floods that created the Channeled Scablands poured into the Grand Coulee. Fig. 127. Grand Coulee Dam on the Columbia River on the Columbia Plateau in west-central Washington.

Snake River Plain and the Yellowstone Hotspot

The Yellowstone Hotspot is associated with a hot mantle plume that is slowly migrating eastward; it is currently beneath the northwestern Wyoming region (Figures 128 to 130). The Yellowstone Hotspot is responsible for a series of great volcanic centers that have linked together to form the Snake River Plain—about 16 million years ago the Yellowstone Hotspot was located under western Oregon. As the hotspot slowly moved eastward under the North American plate it created a series of supervolcanoes that intermittently experienced massive caldera-style eruptions followed by massive floods of basalt that filled the calderas and blanketed the surrounding region, slowly creating the Snake River Plain. The Yellowstone Volcano, one of the world's largest, is currently over the hotspot. Although Yellowstone National Park is most famous for its hotsprings and geysers, the volcano also has a caldera (a massive lava-filled crater) that is 70 miles across. Yellowstone has experienced at least three massive caldera-style eruptions: 2.1 million years ago, 1.2 million years ago and 640,000 years ago, each many hundreds to thousands of times larger than any eruptions in modern history. We can assume more will happen in the future!

Thermopolis, Wyoming claims to have the largest hotsprings in the world. Thermopolis is possibly located over the leading edge of the eastward-moving Yellowstone hotspot. (Figure 131).
Migration of the Yellowstone hotspot Old Faithful Geyser erupting in Yellowstone National Park, Wyoming. Yellowstone Canyon with Lower Falls, Yellowstone National Park, Wyoming. Thermopolis, Wyoming claims to have the world's largest hot springs.
Fig. 128. Migration of the Yellowstone Hotspot and formation of the Snake River Plain across Idaho. Fig. 129. View of Old Faithful Geyser erupting in Yellowstone National Park in northwestern Wyoming. Fig. 130. Grand Canyon of the Yellowstone with Lower Falls, Yellowstone National Park, Wyoming. Fig. 131. Thermopolis, Wyoming claims to have the world's largest hot springs, may be hotspot related.

Colorado Plateau

The Colorado Plateau is an elevated region sandwiched between the Southern Rocky Mountains (to the east) and the Great Basin/Basin and Range province (to the south and west)(Figure 130). The region is famous for its high desert scenery preserved in a large number of national parks.
The entire Colorado Plateau region has risen nearly a mile in the last 20 million years; this has exposed the region to extensive erosion. The Colorado Plateau is actually a series of erosionally-dissected plateaus with elevation tops ranging from 5,000 to 11,000 feet. There are several small mountain ranges within the Colorado Plateau. The highest elevation of 12,700 feet is found in the La Sal Mountains of Utah. The lowest elevation is 2,000 feet in the Grand Canyon of Arizona. The Colorado River and its tributaries have carved many deep and narrow gorges across the region (Figures 132 and 133).

Nearly 200 named sedimentary rock formations of nearly all geologic ages crop out in canyons, escarpments, mesas, and buttes throughout the Colorado Plateau region. The physical properties of the different rock units give rise to the variety of colors, shapes, and erosional characteristics. Mountain ranges of volcanic origin across the region include the La Sal Mountains, Henry Mountains, Abajo Mountains, and Boulder Mountain in Utah. Mountains on the Colorado Plateau in Arizona include the Chuska Mountains and the San Francisco Mountains.
Map showing the location of national parks and monuments on the Colorado Plateau.
Fig. 132. Map showing the location of national parks and monuments on the Colorado Plateau.
Colorado River drainage basin.
Fig. 133. Map of the greater Colorado River Basin which encompasses the Colorado Plateau.

Landscape Features on the Colorado Plateau in Utah

One of Utah's claim to fame is its 5 national parks: Arches, Canyonlands, Capitol Reef, Bryce Canyon, and Zion. However, there is much more to see in Utah if you like high desert canyon country. Arches National Park is famous for its natural arches sculpted into thin finds of Jurassic- age Entrada Sandstone (Figure 134). Canyonlands National Park encompasses the rugged canyon country surrounding the confluence of the Green and Colorado Rivers, the principle rivers dissecting the Colorado Plateau (Figure 135 and 136). The Colorado River drains from the high ranges of Colorado before entering Colorado Plateau Country near Grand Junction. The Green River descends out of Wyoming, cutting a path around the east end of the Uinta Mountains before entering the Colorado Plateau at Dinosaur National Monument on the Colorado-Utah Border (Figure 137). The combined rivers become the principle water supply for the southwestern United States.
Delicate Arch in Arches National Park, Utah. Confluence of the Colorado River and Green River in Canyonlands National Park, Utah The Needles district in Canyonlands National Park, Utah. Green River Canyon in Dinsaur National Monument, Colorado/Utah border.
Fig. 134. Delicate Arch in Arches National Park is an icon for both the State of Utah and the National Park Service. Fig. 135. Confluence of the Green and Colorado Rivers in the heart of Canyonlands National Park, Utah. Fig. 136. The Needles district in Canyonlands National Park, Utah is famous for erosional features of the Permian-age Cedar Mesa Sandstone. Fig. 137. The Green River cuts through a monoclinal fold in Dinosaur National Monument, Colorado/Utah border.
The San Juan River drains from the high country of the San Juan Mountains in Colorado into northern New Mexico, then crosses into southern Utah where it drains into Lake Powell on the Colorado River. Along the way the San Juan River has carved a meandering path called the" Goosenecks of the San Juan" (Figure 138). The Gooseneck reveal that the San Juan River was probably a meandering stream on a broader flood plain before regional uplift increased the stream gradient, forcing the river to carve down into its floodplain. The regional uplift of the Colorado Plateau began about 6 million years ago. The uplift increased the stream gradient in the region, and stream downcutting followed. This phase of uplift and erosion is responsible for nearly all the magnificent landscape features on the Colorado Plateau. Near Mexican Hat (name for both a town and its landmark feature) the San Juan River cuts through late Paleozoic strata exposed in the Riplee Anticline (Figure 139). North of Mexican Hat, Utah Highway 95 passes through the "Valley of the Gods" before it climbs the massive escarpment of the Permian-age Cedar Mesa Sandstone (Figure 140). The Cedar Mesa Sandstone is host to several amazing natural bridges and canyons in Natural Bridges National Monument (Figure 141).
Incised meanders "Goosenecks"of the San Juan River, Utah. Mexican Hat, a famous landmark, with the Riplee Anticline in the distance, southern Utah. Southern Utah Highway 95 descends into the Valley of the Gods, an escarpment along the San Juan River valley. White canyons carved into the Permian Cedar Mesa Sandstone in Natural Bridges National Monument, Utah.
Fig. 138. The "Goosenecks of the San Juan" are a series of incised river meanders on the San Juan River, southern Utah. Fig. 139. Mexican Hat, a famous natural landmark, with the Riplee Anticline in the distance, southern Utah. Fig. 140. Utah Highway 95 descends into the Valley of the Gods, an escarpment along the San Juan River valley. Fig. 141. White canyons carved into the Permian Cedar Mesa Sandstone in Natural Bridges National Monument, Utah.
The Kayenta Formation and Navajo Sandstone (both Lower Jurassic) form high escarpments and deep canyons wherever they crop out on the Colorado Plateau. The Kayenta Formation is mostly a pink or buff-orange sandstone; the overlying Navajo Sandstone typically forms white cliffs. Together they are the rocks that form Rainbow Bridge and many of the high cliffs along Lake Powell and Glen Canyon (below Glen Canyon Dam) (Figures 142 to 144). The Kayenta and Navajo formations are also featured in Zion National Park and Capitol Reef National Park (Figures 145 and 146).
Rainbow Bridge Navajo Mountain, east of Lake Powell in northern Arizona. Glen Canyon Dam Jurassic Navajo Sandstone dominates cliffs in Zion National Park, Utah.
Fig. 142. Rainbow Bridge National Monument on Lake Powell with Navajo Mountain in the distance, located in southern Utah. Fig. 143. Navajo Mountain, southeast of Lake Powell in Glen Canyon National Recreation Area, Utah and Arizona. Fig. 144. Glen Canyon Dam on the Colorado River is within Glen Canyon National Recreation area (near Page, Arizona). Fig. 145. White cliffs of Jurassic Navajo Sandstone over red Kayenta Formation dominates the canyon scenery in Zion National Park, Utah.
View of the Waterpocket Monocline from the Strike-Valley Overlook in Capitol Reef National Park with the Henry Mountains to the east (in central Utah).
Fig. 146. Panoramic view of the Waterpocket Monocline (a great fold in Mesozoic-aged sedimentary rock formations), as seen from the Strike Valley Overlook in Capitol Reef National Park with the Henry Mountains in the distance to the east (in central Utah). The Henry Mountains were the last "discovered" and named mountain range in the United States by the Powell Expedition of 1869. The consist of the eroded remnants of mid-Tertiary igneous intrusions (laccoliths).

Stratigraphy of the Grand Staircase

The name Grand Staircase has been used to describe the step-like nature of cliff-forming escarpments on the Colorado Plateau. The Grand Staircase starts at the Colorado River in Grand Canyon National Park (about 2,000 feet in elevation) and climbs up the stratigraphic section through Grand Staircase-Escalante National Monument, and Zion an Bryce Canyon National Parks (Figure 147). Some rock units are mostly soft shales and mudstone and generally weather to form slopes. Hard limestone and sandstone formations tend to form clifts and cap escarpments and plateau tops, such as the Kaibab Limestone capping the Kaibab Plateau around the Grand Canyon. Every rock formation has a distinct appearance associated with their composition and origin. However, cliff-forming formations have been named by early settlers in the region including the Chocolate Cliffs (Moenkopi Formation), Vermillion Cliffs (Moenave/Kayenta Formations), White Cliffs (Navajo Sandstone), Gray Cliffs (Cretaceous formations), and Pink Cliffs (Claron Formation). See more at Stratigraphy of the Colorado Plateau.
Stratigraphy of the Grand Staircase, Arizona and Utah.
Fig. 147. Stratigraphy of the Grand Staircase, Arizona and Utah.

High Plateaus of Central Utah

The western side of the Colorado Plateau consists of a series of high plateaus with elevations ranging from 8,000 to over 11,000 feet and include the Sevier, Aquarius, Paunsaugunt, Kaiparowitz, and Markagunt Plateaus, and Boulder Mountain (a volcano). The western side of these plateaus transition into the Wasatch Mountains along the border of the Colorado Plateau and the Great Basin to the west. The boundary region has many active earthquake faults that are responsible for the rugged topography of the Transition Zone between provinces (Figure 148). The fault zones are also associated with regional volcanic activity during the Pleistocene Epoch. Ancient lake deposits of Eocene-age Claron Formation now cap the highest part of the plateaus (Figures 149 and 150).
Utah Fault and Rivers.Fig. 148. Utah faults and rivers. Bryce Canyon, Utah Cedar Breaks National Monument.
Fig. 149. The Eocene-age Claron Formation forms the Pink Cliffs and caps the Paunsaugunt Plateau at Bryce Canyon National Park. Fig. 150. Badlands in the Eocene-age Claron Formation in Cedar Breaks National Monument located along the western escarpment of the Markagunt Plateau, Utah.

Colorado Plateau in Arizona

The Colorado Plateau extends into northern Arizona—most of the region in Arizona is on the Navajo and Hopi Indian Nation lands, mostly remote, often rugged high-desert country (Figure 151). The region is characterized by broad plains and plateaus. The physiography of the region is primarily defined by physical characteristics of the bedrock geology (Figure 152). Regional uplift has resulted in erosion that has carved carved canyons, escarpments along the Colorado River and its tributaries. In addition volcanism and tectonic forces have shaped the landscape in Tertiary time to the present. Precambrian and Paleozoic rocks are exposed in the Grand Canyon and the Defiance Uplift region. Elsewhere, Permian, Triassic, Jurassic, and Cretaceous sedimentary rock formations form escarpments and associated plateaus across the region.
Physiography of Arizona
Fig. 151. Arizona physiography.
Geologic Map of the southern Colorado Plateau Region showing rock units by geologic age and composition.
Fig. 152. Geologic Map of the southern Colorado Plateau Region showing rock units by geologic age and composition, volcanic, faults, and folds.

The Grand Canyon

The Grand Canyon is the largest and deepest canyon in the United States. The canyon cuts through the Kaibab Uplift (or Kaibab Plateau) for a distance of almost 300 miles. It varies from 4 to 16 miles wide, and about 1 mile deep (Figure 153). The Grand Canyon starts where the Colorado in Marble Canyon joins the Little Colorado River (Figure 154). The lower canyon ends where it joins the Virgin River in Lake Mead. Crystalline basement rocks, sedimentary rocks, and volcanic rocks of Precambrian age crop out along the Inner Gorge (Figure 155). Flat-lying sedimentary rock formations of Cambrian to Permian age form the Paleozoic section of the Grand Staircase (see Figure 156). The Colorado River and its tributaries have carved the Grand Canyon as the Kaibab Uplift has risen over the past 6 million years. The Kaibab Uplift is an erosionally dissected plateau. The South Rim is averages about 6,800 feet, the North Rim averages about 8,300 feet, the Colorado River averages about 2,200 feet (Figures 157 to 158).
Satellite view of the Grand Canyon and Kaibab Plateau, northern Arizona.
Fig. 153. Satellite view of the Grand Canyon cutting through the Kaibab Uplift (Plateau) in northern Arizona.
Marble Canyon Bridge located just downstream from Lees Ferry, Arizona.
Fig. 154. Marble Canyon Bridge located just downstream from Lees Ferry, Arizona and upstream of the Grand Canyon.
Grand Canyon's Inner Gorge as seen from the Bright Angel Trail. Grand Canyon Rock fins and butte in the Kaibab Limestone at Roosevelt Point along the North Rim of Grand Canyon National Park. Lava flows poured into a dammed the Grand Canyon many times during the Pleistocene Epoch.
Fig. 155. Grand Canyon's Inner Gorge near Phantom Ranch as seen from the Bright Angel Trail in Grand Canyon National Park.
Fig. 156. South Rim view of the Colorado River and Kaibab Plateau on the North Rim in Grand Canyon National Park, Arizona. Fig. 157. Rock fins and butte in the Kaibab Limestone at Roosevelt Point along the North Rim of Grand Canyon National Park. Fig. 158. Lava flows poured into a dammed the lower Grand Canyon many times during the Pleistocene Epoch.

Permian escarpments

The majestic buttes and mesas of Monument Valley and Canyon De Chelley formed erosion of the Permian-age De Chelley Sandstone (Figures 159 and 160). Canyon de Chelley is carved into The Defiance Uplift—a north-south trending anticline extending over 100 miles from the Four Corners region to Interstate 40, just inside the Arizona border (Figure 161). The southern boundary of the Colorado Plateau is the Mogollon Rim, an escarpment capped by Permian-age Kaibab Limestone and Coconino Sandstone, and locally by Tertiary basalt flows. The escarpment rises about 3,000 feet above low lands south of the rim in the mountainous “transition zone" between the Colorado Plateau and the Basin and Range (example is at Sedona, Arizona, Figure 162).

Triassic plains and badlands

The Painted Desert is a region underlain by the brightly colored mudstone and shale of the Triassic-age Chinle Formation, forming badlands topography in the high desert climate (Figures 163 and 164). The Chinle Formation is host to fossiliferous beds exposed in Petrified Forest National Park and throughout the Painted Desert region.

Mesozoic escarpments and Plateaus

High, steep cliff-sided escarpments form along exposures of Kayenta, Navajo, and Entrada Sandstone formations (Figures 165 to 166). Black Mesa is a high plateau region underlain by Cretaceous-age sedimentary rocks that have abundant coal resources.
Remnants of Permian sedimentary rocks exposed in Monument Valley on the Navajo Reservation, Arizona. Spider Rock in Canyon de Chelley, Arizona A monoclinal fold in Permian strata along the Defiance Upwarp near Window Rock, Arizona. Cliffs and buttes around Sedona, Arizona are part of the southern escarpment of the Colorado Plateau called the Mogollon Rim. is the
Fig. 159. Remnants of Permian sedimentary rocks exposed in Monument Valley on the Navajo Reservation, Arizona. Fig. 160. Spider Rock in Canyon de Chelley National Monument, eastern Arizona. Fig. 161. A monoclinal fold in Permian strata along the Defiance Upwarp near Window Rock, Arizona. Fig. 162. Cliffs and buttes around Sedona, Arizona are part of the southern escarpment of the Colorado Plateau called the Mogollon Rim.
Painted Desert in northern Petrified Forest National Park, Arizona/New Mexico border. Adeii Eechii Cliffs are an escarpment between Flagstaff and Tuba City, Arizona. Anasazi ruins are in an alcove in Kayenta Formaiton beneath Navajo Sandstone in  Navajo National Monument, AZ. Coal Mine Mesa near Tuba City, AZ has a cap of Cretaceous Dakota Formation over cliffs of Jurassic Entrada Sandstone.
Fig. 163. Painted Desert in Triassic Chinle Formation exposed in northern Petrified Forest National Park, Arizona/New Mexico border. Fig. 164. Adeii Eechii Cliffs are an escarpment of Jurassic sandstones over Triassic shale badlands located between Flagstaff and Tuba City, Arizona. Fig. 165. Anasazi ruins are in an alcove in Kayenta Formation beneath Navajo Sandstone in Navajo National Monument, Arizona. Fig. 166. Coal Mine Mesa near Tuba City, Arizona has a cap of Cretaceous-age Dakota Formation over cliffs of Jurassic Entrada Sandstone.

Igneous Rock Features on the Colorado Plateau

Volcanic features on the Colorado Plateau in Arizona have formed in stages through Tertiary time to the present. Erosional remnants of ancient volcanic features stand out in stark dark contrast to the surrounding brightly colored sedimentary rocks. Three regions where igneous rocks crop out include the Navajo, Hopi Buttes, and San Francisco Volcanic Fields.

The Navajo Volcanic Field includes scattered features in Four Corners Region extending from near Kayenta, Arizona into the Carrizo Mountains and region surrounding the Four Corners (AZ, NM, CO and UT). Volcanic vents are also scattered around in the Chuska Mountains (northwest Arizona) (Figure 167).

The Hopi Buttes consist of eroded remnants of igneous dikes, stocks, volcanic breccia, and diatremes that formed about 25 to 30 million years ago. The Hopi Buttes Volcanic Field northeast of Holbrook, Arizona consists of eroded remnants of volcanic features that formed between 8.5 to 4.2 million years ago (Figure168).

The San Francisco Volcanic Field is located north and west of Flagstaff, Arizona and contains 600 volcanoes ranging in age from about 6 million years to the youngest less than a 1,000 years. Humphreys Peak (elevation 12,633 feet) is a large stratovolcano near Flagstaff and is Arizona’s highest peak (Figure169). Wupatki-Sunset Crater National Monument is host to the youngest volcano and lava flows about 900 years old (Figure 170).

A volcanic stock (a kimberlite) near Kayenta, Arizona. Hopi Buttes, Humphreys Peak, elevation Sunset Crate, a cinder cone with lava flows that formed
Fig. 167. A volcanic stock (a kimberlite) near Kayenta, is part of the Navajo Volcanic Field, northeastern Arizona. Fig. 168. Hopi Buttes are eroded remnants of a Miocene-age volcanic field in the Painted Desert region of Arizona. Fig. 169. Humphreys Peak, elevation 12,625 feet, is Arizona's highest peak in the San Francisco Volcanic Field. Fig. 170. Sunset Crater, a cinder cone with lava flows that formed about 900 years ago in the San Francisco Volcanic Field.

Colorado Plateau in Colorado

The Colorado Plateau extends partly into western Colorado (Figure 171). Along Interstate 70, the transition from the Rocky Mountains to the Colorado Plateau occurs near Glenwood Springs, Colorado. West of Glenwood Springs the Colorado River canyon expands into the broad Grand Valley near Grand Junction, Colorado. (Note: in 1921, Congress changed the name of the Grand River to Colorado River!)

On the north side of the Grand Valley are the Book Cliffs, an escarpment to the Roan Plateau.The Roan Plateau overlies the Piceance Basin, a structural downwarp filled with early Tertiary-age sediments that underlies the region between northwestern Colorado to Green River in northern Utah. The Book Cliffs are an escarpment of the Green River Formation (Eocene) which are host to massive shale-oil resources (estimated to be more than all oil reserves in the OPEC nations). Those deposits, however, are not economically feasible to extract.

On the south side of the Grand Valley is an escarpment composed of Mesozoic-age rock formations borders the south side of the Colorado River Valley, much of it is preserved in Colorado National Monument (Figures 172 and 173). The escarpment is the northern border of the Uncompahgre Plateau, an expansive upland region with elevations averaging about 9,500 feet. The Uncompahgre Plateau borders the San Juan Mountains to the southeast. Most of the bedrock exposed in the Colorado Plateau south of the Colorado River is Cretaceous sediments of the Mancos Shale and overlying Mesa Verde Formation.

Mesa Verde is another upland plateau located the southwestern corner of Colorado. The Plateau is host to Mesa Verde National Park (Figures 174 and 175). Nearby is Hovenweep National Monument (near Sleeping Ute Mountain, a volcanic laccolith). Both parks preserve notable ruins from the Anasazi (ancestral Pueblo Cultures).
Map of Western Colorado.
Fig. 171. Map of western Colorado showing the border between the Rocky Mountains Province and the Colorado Plateau Province.
Escarpments of Cretaceous sedimentary rocks in Colorado National Monument and the Colorado River Valley near Grand Junction, Colorado. A large monoclinal fold along the north side of the Uncompaghre Plateau and the south side of the Grand Valley near Grand Junction in Colorado National Monument. Ancient Anasazi cliff dwellings in overhanging Cretaceous-age sedimentary rocks in Mesa Verde National Monument, Colorado Coal beds in the Cretaceous Mesaverde Formation on Mesa Verde, Coloraodo.
Fig. 172. Escarpments of Mesozoic-age sedimentary rocks in Colorado National Monument and the Colorado River Valley near Grand Junction, Colorado. Fig. 173. A large monoclinal fold along the north side of the Uncompahgre Plateau and the south side of the Grand Valley near Grand Junction in Colorado National Monument. Fig. 174. Ancient Anasazi cliff dwellings are preserved in an alcove in overhanging Cretaceous-age sedimentary rocks in Mesa Verde National Park, Colorado. Fig. 175. A road cut along the road to Mesa Verde National Park exposes coal beds and river sand beds in the Cretaceous Mesaverde Formation.

Colorado Plateau in New Mexico

The Colorado Plateau extends partly into northwestern New Mexico. The San Juan River is the main river drainage in the region. The San Juan Basin is a structural basin that encompasses most of the New Mexico portion of the Colorado Plateau (see Figure 152). The region around Farmington, New Mexico is an old oil and gas producing basin. The region is perhaps most famous for Chaco Canyon National Historic Park, a park that encompasses several ancestral Pueblo Indian (Anasazi) cities, long abandoned, along Chaco Wash, a tributary of the San Juan River (Figure 176).

Ship Rock is a prominent natural landmark that rises from the San Juan Basin along the New Mexico/Arizona border. Shiprock is the eroded remnant of an ancient volcano—only the volcanic stock with wall-like radiating dikes remain (Figure 177). It is an outlier of the Navajo Volcanic Field that extends into Arizona.
El Mal Pais National Monument and El Morro National Monument are parks along the southern border of the Colorado Plateau. El Mal Pais (Spanish for "badlands") is a valley that was flooded by basaltic lava flows from eruptions from the Zuni-Bandera Volcanic Field (Figure 178). Volcanic eruptions have occurred as recently as 3,000 years ago. El Morro National Monument is also host to a historic natural landmark called Inscription Rock. Plunge pools at the base of waterfalls draining from Inscription Rock was a source of water along ancient and historic trails across the region. Ancestral and modern Indians, early Spanish explorers, Army soldiers, and early settlers all carved messages into the soft Aztec Sandstone that makes up the rock (Figure 179).
Chaco Canyon National Historical Park, New Mexico Ship Rock El Mal Pais El Morro Inscription Rock at El Morro National Monument.
Fig. 176. Chaco Canyon National Historical Park, New Mexico Fig. 177. Ship Rock in western New Mexico is an eroded volcanic stock with dikes. Fig. 178. El Mal Pais National Monument. Fig. 179. Inscription Rock at El Morro National Monument.

Basin and Range Provinces

Basin and Range is the term used to describe the general topography of a vast region of the Western Cordillera extending from southern Oregon to West Texas (Figure 180). The Basin and Range is subdivided into three physiographic Provinces. In the north is the Great Basin, a vast region of mountain ranges and low desert valleys that has no external drainage connection to the ocean. The Mojave Desert region encompasses parts of southern California and southern Nevada. In the southeast is the province name Basin and Range that extends from the Colorado River west across southern Arizona, New Mexico, into West Texas.

The Basin and Range is generally characterized by north-to-south trending mountain ranges with intervening valleys. Valley elevations range from below sea level to about 2,000 feet, mountain ranges average about 7,000 feet with several rising above 12,000 feet. The basin and range topography is a result of crustal extension associated with the plate-tectonic history of western North America (see Figure 102). Starting about 25 million years ago, the North America Plate gradually moved over a spreading center that separated the ancient Farallon Plate from the Pacific Plate. The spreading center is now underneath the Basin and Range Province, causing it to gradually spread apart (Figure 181).

Great Basin and Basin & Range regions Geologic structures associated with crustal compression and extension.
Fig. 181. Geologic structures associated with crustal compression and extension. Basin and Range provinces have experience crustal extension gradually over the past 18 million years.
Fig. 180. Map of the Basin and Range Provinces: Great Basin, Mojave, and Basin and Range sub provinces.
Since about 18 million years ago, the Basin and Range has slowly expanded as the Sierra Nevada Range has slowly moved north and west relative to the rest of the western North American craton (Rocky Mountains and Colorado Plateau regions). This caused the Basin and Range region to stretch apart (crustal extension). What started as continental rifting translated into the splitting of the crust into a series of large, parallel, crustal blocks that gradually rotated, creating a horst-and-graben structure—much like books sliding against each other as they fall over on a shelf. Estimates are the the Basin and Range has expanded by as much as 300 miles. The eastern and western margins of the Great Basin are generally where most tectonically is actively occurring, but great earthquakes have happened all across the region. Volcanism has also generally followed the rifting along the margins of the basin, especially where it gradually expands eastward.

The Basin and Range provinces encompasses four desert regions of North America including the Great Basin, Mojave, Sonoran, and Chihuahuan deserts (Figure 182). The highest ranges typically have pine forests, and mixed evergreen and deciduous forests. In contrast, during the peak of the Pleistocene ice ages, the region was wetter, and great lakes filled many of the low, internally drained basins across the region (Figure 183).
Desert and steppe regions in the Western United States
Fig. 182. Deserts and steppe regions of North America.
Pleistocene lakes of the Great Basin region
Fig. 183. Pleistocene Lakes in the Great Basin and Mojave.

Great Basin Province

The Great Basin Province encompasses most of Nevada and parts of southern Oregon, western Utah, and parts of eastern California (see Figure 180). The physical geography of the region is well illustrated in Great Basin National Park, Nevada. The park displays a great range of ecological diversity ranging from grasslands and sagebrush desert to high alpine tundra, to high alpine tundra, with many ecozones and habitats in between (Figures 184 to 186). Most of Nevada is open rangeland. Highway 50 that crosses east-west across Nevada is called the "Loneliest Road in America" (in competition with Highway 93 that runs north-south across the state). Besides gambling and entertainment (Las Vegas style), the Great Basin region has a long history of ranching and mining development, primarily gold, silver, and other metals.
Great Basin sagebrush desert in the valley east of the Snake Range in Great Basin National Park, Nevada. Wheeler Peak in Great Basin National Park, Nevada Bristlecone pines  on Wheeler Peak in Great Basin National Park have lived thousands of years in relatively cold, hostile conditions. A historic gold mine in Berlin-Itchyosaur National Monument, central Nevada.
Fig. 184. High peaks of the Snake Range rise above sagebrush desert in Hamlin Valley in Great Basin National Park, Nevada. Fig. 185. Wheeler Peak (elevation 13,064 feet) is part of a glaciated highlands in the Snake Range in Great Basin National Park, Nevada. Fig. 186. Bristlecone pines on Wheeler Peak in Great Basin National Park have lived thousands of years in relatively cold, hostile conditions. Fig. 187. A historic gold mine and a fossil marine reptile mine both are preserved in Berlin-Itchyosaur State Park, central Nevada.
Traveling across the Great Basin is it easy to see remnants of the ancient shoreline features of the great lakes that once filled most of the basin areas (see Figure 183). Ancient Lake Lahonton filled the basins in western Nevada to depths as much as 900 feet at the peak of the last ice age, and was one of the largest lakes in North America. Mono Lake (east of Yosemite National Park) in California is a salt lake fills a valley that was once was a much greater drainage system that ended in Death Valley (Figure 188). The Great Salt Lake, Utah was once part of ancient Lake Bonnieville—at one time it was about 1,000 feet deep and perhaps the largest freshwater lake in the world. Today the lake is only 33 feet deep at its deepest point, and the western portion is now the Bonnieville Salt Flats (Figure 189).

The region north of the Great Salt Lake is transitional to the Rocky Mountains, having characteristics of both provinces and has important history. Early settlers skirted around the rugged and arid lands of the Great Basin by following the California Trail (part of the route is preserved at City of Rocks National Reserve where trails converged near what is Almo in southern Idaho, Figure 190). The California Trail was heavily traveled in the summers from 1845 to 1869. History was then made at Promontory Point, a low range on the north side of Great Salt Lake where where in 1869 the Central Pacific Railroad Company of California (building east) joined the Union Pacific Railroad (building west), forming the First Transcontinental Railroad (now Golden Spike National Monument, Figure 191).
Mono Lake, a interally-drained basin on the west side of the Sierra Nevada that is 4-times saltier than the ocean. Great Salt Lake covers the low eastern basin of the Great Basin. Cretaceous-age granitic intrusions exposed in City of Rocks National Monument, Idaho. Golden Spike NM is where the Transcontinental Railroad was completed in 1867.
Fig. 188. Tufa towers in Mono Lake, a internally-drained basin on the west side of the Sierra Nevada that is 4-times saltier than the ocean. Fig. 189. Great Salt Lake covers the low eastern basin of the Great Basin west of the Wasatch Mountain front near Salt Lake City. Fig. 190. Cretaceous-age granitic intrusions exposed in City of Rocks National Reserve, Idaho located in the transition zone with Rocky Mountains. Fig. 191. Golden Spike NM (north of Great Salt Lake, Utah) is where the First Transcontinental Railroad was completed in 1869.

Mojave Desert Province

The Mojave Desert Province encompasses a large portion of southern California and small parts of southern Nevada, Utah, and northwestern Arizona. The Mojave Desert displays basin and range topography, but differs from the rest of the Basin and Range Provinces based on geographic, climate, and biological factors.

The north and boundaries of this triangular-shaped region is are basically topographic features associated with major faults in California, the Garlock Fault runs east-west along the south side of the Tehachapi Mountains. The south and side of the desert and the San Andreas Fault basically defines the boundary along the San Gabriel Mountains and San Bernardino Mountains (Figure 192). North and east is the Colorado Plateau and the Basin and Range Province of southern Arizona which is part of the Sonoran Desert.

Like the Great Basin region to the north, the Mojave Desert Province is partly an internally drain basin region. During the last ice age, Mono Lake basin (ancient Lake Russell) drained through ancient lakes in Owens Valley, Panamint Valley, Searles Valley, and finally into Death Valley that was flooded by ancient Lake Manly to a depths as much as 600 feet. Today, the basins are host to dune fields and dry lake beds that only flood temporarily during intermittent wet periods. Further south, the ancestral Mojave River flowed into ancient Lake Mannix through a series of basins. Soda Lake and Silver dry lakes near Baker California are remnants of that drainage system (Figure 193). The Colorado River has also drained into the internal basins of southern California in the past, most recently into the Salton Sea. The Salton Sea basin is a small remnant of the much larger Ancient Lake Chauilla. The modern Salton Sea was artificially created when in floods on the Colorado River in 1905 to 1907 broke through diversion canals in the irrigation system. 

The Mojave Desert is host to several large national parks including Death Valley National Park, Glen Canyon National Recreation Area, the Mojave National Preserve, and Joshua Tree National Park.

Ancient lakes and rivers in the Mojave Desert region.
Fig. 192. Ancient lakes and Rivers of the Mojave Desert region.
Soda Dry Lake near Baker, CA.  Fig. 193. Soda Dry Lake near Baker, California.

Death Valley

Death Valley National Park is along the west side of the Great Basin in southern California in the transition zone to the Mojave Desert Province (it has characteristics of both regions. The deep valley is located in the rainshadow region of the Sierra Nevada Range and is typically averages among the hottest and driest place in North America (Figures 194 to 197). The name Badwater has been assigned to the salt pan located in southern Death Valley—the lowest spot in North America with an elevation of -282 feet. In contrast, Telescope Peak, the highest peak of the Panamint Range adjacent to Death Valley, has an elevation of 11,043 feet. Parts of Death Valley are also considered as part of Mojave Desert Province.
Dantes View in the Funeral Range gives a good view of Death Valley, California. Badwater (elevation - Panamint Valley with Panamint Dunes in Death Valley National Park, California. Racetrack Playa is in a valley high in the Cottonwood Mountains, Nelson Range next to Saline Valey in the distance.
Fig. 194. Dantes View in the Funeral Range gives a good view of Death Valley in Death Valley National Park, California. Fig. 195. Badwater (elevation -282 feet) is next to the Funeral Range in Death Valley is the lowest place in North America. Fig. 196. Panamint Playa with Panamint Dunes and Hunter Mountain in Death Valley National Park, California. Fig. 197. Racetrack Playa in the Cottonwood Mountains, Nelson Range next to Saline Valley in the distance.
Lake Mead National Recreation Area encompasses lands along the Colorado from below Grand Canyon National Park to Bullhead City Arizona (Figures 198 to 201). Lake Mead is the reservoir behind Hoover Dam, a 726-foot tall dam constructed in 1931-1936 during the Great Depression. The dam was built in upper Black Canyon. Below Black Canyon the Colorado flows into Lake Mojave, the reservoir for behind Parker Dam, constructed in 1934-1938.
Uplifed sedimentary rock layers along the eastern margin of the Great Basin along the Colorado River west of the Grand Canyon. Black Canyon, located along the Colorado River between Nevada and Arizona south of Hoover Dam. Hoover Dam in Black Canyon along the Colorado River, located south of Las Vegas in the Lake Mead National Recreation Area. Lake Mojave is a Colorado River reservoir located south of Black Canyon along the
Fig. 198. Uplifted sedimentary rock layers along the eastern margin of the Great Basin along the Colorado River west of the Grand Canyon. Fig. 199. The Colorado River has carved Black Canyon in Black Mountains volcanic complex of Tertiary age. Fig. 200. Hoover Dam in Black Canyon along the Colorado River, located south of Las Vegas in the Lake Mead National Recreation Area. Fig. 201. Lake Mojave on the Colorado River between Arizona and Nevada south of Las Vegas and north of Bullhead City, AZ.

Mojave National Preserve

The Mojave National Preserve encompasses a large portion of the Mojave Desert region in southern California. The preserve has a great variety of landscape features (Figure 203 to 207). Cinder Cone National Geologic Landmark is within the preserve, a cinder cone within the Cima Volcanic Field. The Providence Mountains are composed of a thick sequence of Paleozoic-age formations (mostly limestone and dolomite) of the the ancient North American continental margin basin. Kelso Dunes is a massive dune field that formed down wind from the deposits of the Mojave River and ancient Lake Mannix (in the Soda Lake basin area). The Granite Mountains are part of a massive igneous batholith similar in age and origin to the Sierra Nevada (about 180 to 80 million years). Cima Dome is a massive landscape feature that stands out along Interstate 15 between Baker CA and Las Vegas. It is a massive granitic mountain that has eroded down over many millions of years to a nearly perfect symmetrical pediment surface.
A Joshua Tree forest on Cima Dome in the Mojave National Preserve, California.
Fig. 202. A Joshua Tree forest on Cima Dome in the Mojave National Preserve, California.
Cinder Cone National Geologic Landmark, a young volcano in the Mojave National Preserve, California Early Paleozoic sedimentary rocks crop out in the Providence Mountains within the Mojave National Preserve, California. Kelso Dunes in the Mojave National Preserve, one of many large dune fields in the desert regions of southern California. Spheroidally-weathering boulders in the Granite Mountains within the Mojave National Preserve.
Fig. 203. Cinder Cone National Natural Landmark in the Mojave National Preserve, southern California. Fig. 204. Early Paleozoic sedimentary rocks crop out in the Providence Mountains within the Mojave National Preserve, California. Fig. 205. Kelso Dunes in the Mojave National Preserve, one of many large dune fields in the desert regions of southern California. Fig. 206. Spheroidally-weathering boulders in the Granite Mountains within the Mojave National Preserve.
Cima Dome in the Mojave National Preserve is a 1,500 foot high granitic mountain that has eroded down to its nearly perfectly symmetrical pediment surface. It is host to the most extensive forest of Joshua Trees in the region.
Fig. 207. Cima Dome in the Mojave National Preserve is a 1,500 foot high granitic mountain that has eroded down to its nearly perfectly symmetrical pediment surface. It is host to the most extensive forest of Joshua Trees in the region.

Joshua Tree National Park

“High Desert” regions in the Mojave Desert are above elevations of about 2,000 feet, and are expressed by the presence of indicator plants: Joshua Trees (Yucca brevifolia) (most common in elevations 5,000 to 7,000 feet) (Figure 208). “Low Desert” below 2,000 feet are part of the Sonoran Desert ecosystem, mostly limited to the south and along the lower Colorado River valley.
Whereas Joshua Trees are an indicator plant for the "High Desert", Teddy Bear Cholla (Cylindropuntia bigelovii) , the indicator plant for the "Low Desert" in the Mojave Desert region (most common between 1,000 to 3,000 feet) (Figure 209).

Joshua Tree National Park located in the Little San Bernardino Mountains, an uplifted plateau region along the eastern margin of the Mojave Desert Province bordering the Colorado Desert. High parts of the plateau are above 5,000 feet (the highest point, Quail Mountain, elevation 5,813 feet). Joshua Tree National Park is a famous destination for rock climbers—there are cliffs and boulder piles consisting hard granite scattered throughout the park (Figures 210 and 211). Figure 212 illustrates an exfoliating granite pluton on the northeast flank of Ryan Mountain. Domes like this in the park are remnants of Mesozoic-age molten rock material that melted or injected its way upward into more ancient bedrock of gneiss and schist. As the mountains rose, erosion kept pace, stripping away perhaps miles of rock, exposing the plutons.

The Little San Bernardino Mountains are on the east side of the Coachella Valley, rift valley of the San Andreas Fault (Figure 213). In contrast to the high ranges along the margins, the Coachella Valley is quite low—Palm Springs, California is below 500 feet, and the Salton Sea to the south is -226 feet (and falling as it dries up). The Coachella Valley and Salton Sea are part of the Colorado Desert Province.

A Joshua Tree in Joshua Tree National Park.Fig. 208. A Joshua Tree in Joshua Tree National Park, southern California.
Teddy-Bear Cholla forest in Pinto Basin in Joshua Tree National Park. Fig. 209. A Teddy-Bear Cholla forest in Pinto Basin in Joshua Tree National Park.
Piles of large granite boulders are a common sight throughout Joshua Tree National Park. Boulder piles rise above a pediment surface in Joshua Tree National Park. A granite igneous pluton exposed by erosion on Ryans Peak, Joshua Tree National Park, CA. San Jacinto Peak and Coachella Valley from Keyes View in Joshua Tree National Park, CA.
Fig. 210. Piles of large granite boulders occur throughout Joshua Tree National Park are a popular destination for rock climbers. Fig. 211. Boulder piles (eroded tops of granite plutons) rise above a pediment surface in Lost Horse Valley in Joshua Tree National Park. Fig. 212. An exfoliating granite pluton of Mesozoic age rises above surrounding softer eroding bedrock on Ryans Peak in Joshua Tree NP. Fig. 213. Coachella Valley and San Jacinto Peak as seen from Keyes View (looking north) in Joshua Tree National Park, CA.

Colorado Desert Province

The Colorado Desert is a small province in Southern California located in the rift valley the San Andreas Fault the Salton Sea Trough. The province is low desert relative to the the surrounding high ranges on either side. The Little San Bernardino Mountains, Orocopia Mountains, and Chocolate Mountains border the east side of the valley (the western border escarpment of the Mojave Desert Province). The north end of the province is the Coachella Valley, the southern end is the Imperial Valley that encompasses the Salton Sea extends south to the Gulf of California (Figure 214 to 217).

The Salton Sea has flooded and dried up many times in the recent geologic past. Sediments filling the lower Colorado River Drainage have diverted Colorado River away from the Gulf of California and into the Salton Basin. Ancient Lake Cahuilla formed and persisted from around 700 A.D. to about 1700 A.D. The modern Salton Sea formed in 1905 when Colorado River flood waters broke through irrigation control levees, allowing water to flow into the basin freely for 18 months. The lake is now supplied by irrigation drainage waters. Anza Borrego State Park is the largest state park in the United States (Figures 217 to 218)
Colorado Desert is a low region east of the Peninsular Ranges and north of the Gulf of California.
Fig. 214. Colorado Desert is a low region east of the Peninsular Ranges and north of the Gulf of California.
Desert fan palms grow near springs along the San Andreas Fault scarp in the Coachella Valley Preserve near Palm Springs, CA. View looking south along the Coachella Valley towards the Salton Sea basin. Anza Borrego Desert in eastern San Diego County is part of the Colorado Desert Province.
Ocotillo and barrel cactus are common plants in the natural cactus gardens in the Anza Borrego Desert. cactus gar
Fig. 215. Desert fan palms grow near springs along the San Andreas Fault scarp in the Coachella Valley Preserve near Palm Springs, CA. Fig. 216. View looking south along the Coachella Valley towards the Salton Sea basin and Imperial Valley region. Fig. 217. Anza Borrego Desert in eastern San Diego County is part of the Colorado Desert Province. Fig. 218. Ocotillo and barrel cactus are common plants in the natural cactus gardens in the Anza Borrego Desert.

Basin and Range Province

The rugged basin and range landscape of southern Arizona, New Mexico and West Texas is assigned the name Basin and Range Province (Figure 219). The physiography region extends into northern Mexico continues bordered on the south by the Mexican Highlands and eastern and western Sierra Madre Ranges in Mexico.

The Basin and Range Province experienced mountain building and volcanism during the Laramide Orogeny, the mountain building began about 70 million years ago and extensive volcanism followed between about 35 to 25 million years ago. Crustal extension followed beginning about 18 million years ago, resulting in the Basin and Range structure of the region. Volcanism has occurred in stages, with young volcanic centers of Pleistocene and age are scattered along the eastern margin of the Basin and Range along the Rio Grande Rift Valley. Valles Caldera is part of a supervolcano in the Jemez Volcanic Field around Los Alamos, New Mexico. The super volcano had caldera-forming eruptions 1.5 and 1.1 million years ago, with most recent eruptions 50-60,000 years ago (Figure 220). The Rio Grand River flows down the Rio Grand Rift Valley runs north-to-south along the eastern margin of the Basin and Range Province. The rift valley began forming 35 million years ago and is still active, as evidence by earthquake activity and volcanism as recently as 5,600 years ago. Laramide volcanism features are preserved in Chiracahua National Monument in southeastern Arizona (Figure 221).

The western Arizona part of the region is part of the Sonoran Desert, the eastern part is part of the higher and dryer Chihuahuan Desert. The region is part of the Greater Basin and Range Province that is undergoing crustal extension (producing the horst and graben structure associates with its north-south trending mountain ranges and valleys)(see Figures 180 to 181). The Sonoran Desert wraps around the northern end of the Gulf of California and extends northward along the lower Colorado River and into the low surrounding valleys (including those occupied by Phoenix and Tucson, Arizona). The Saguaro Cactus (Carnegiea gigantea) is an indicator plant for the Sonoran Desert—forests of them are a highlight of Saguaro National Park near Tucson, Arizona (Figure 222).

Big Bend National Park is at the eastern end of the Basin and Range Province in West Texas. Big Bend gets its name from the great bend in the Rio Grand River here it has carved canyons as the ranges and landscape has gradually risen in the region (Figure 223). The Chisos Mountains are another volcanic center associated with the end of the Laramide Orogeny, about 33 to 28 million years ago (Figure 224).
Map of the Basin and Range Province: Arizona, New Mexico, and West Texas.
Fig. 219
. Map of the Basin and Range Province: Arizona, New Mexico, and West Texas.
Valles Caldera is in the center of the supervolcano that makes up the Jemez Mountains near Los Alamos, New Mexico.
Fig. 220. Valles Caldera is in the center of the supervolcano that makes up the Jemez Mountains near Los Alamos, New Mexico.
Hoodoos in volcanic rocks exposed in Chiricahua National Monument, New Mexico Cactus gardens of Suguaro National Park in the Tucson, Arizona area. Rio Grande River in Boquillas Canyon in Big Bend National Park along the Texas-Mexico border. Chisos Mountains in Big Bend National Park, Texas.
Fig. 221. Hoodoos in eroding volcanic rocks exposed in Chiracahua National Monument, New Mexico. Fig. 222. Saguaro Cactus forests are featured in Saguaro National Park near the Tucson, Arizona area.
Fig. 223. Rio Grande River in Boquillas Canyon in Big Bend National Park along the Texas-Mexico border. Fig. 224. Chisos Mountains are the core of a large Tertiary-age volcanic complex located in Big Bend National Park, Texas.

Western Cordilleran and Coast Ranges

The West Coast (Washington, Oregon, and California) is an active continental margin with all the associated geologic features: mountains, rugged coastlines, volcanoes, and earthquakes. Collectively the mountains in the region are called part of the greater Western Cordilleran, but the region is subdivided into several provinces based on both geography and geology. The regional geology is directly related to the plate tectonics of the region (Figure 225). In the north, the Juan de Fuca Plate is actively being subducted beneath northern California, Oregon, Washington, and British Columbia. This subduction is resulting in the formation of the series of volcanoes that make up of the Cascade Ranges that run roughly parallel to the Pacific coast, but about 70 to 120 miles inland from the coastline. Between the Cascades and the Pacific shoreline are the Pacific Borderlands and Coast Ranges.

The San Andreas Fault System is the major feature controlling the geology and geography of California. North of where the San Andreas Fault runs out to sea at Cape Mendicino, subduction is still actively consuming the Juan de Fuca Plate along the Cascadia Subduction Zone. South of Cape Mendicino part of the North American Plate has split away and is now attached to the Pacific Plate and as being carried northward on the west side of the San Andreas Fault. The rate and amount of movement movement can be seen how the Baja Peninsula has been rifted away from Mexico. The rifting open the Gulf of California basin starting about 23 million years ago as the North American Plate gradually moved westward over a spreading center between the ancient Farallon Plate and the Pacific Plate. The change of the relative plate motions of the 3 plates resulted in the formation of the San Andreas Fault system as the Farallon Plate vanished beneath North America. The Juan de Fuca and Cocos Plates are remnants of the once large Farallon Plate.
Major plate tectonic features of the West Coast of the Western United States and Mexico.
Figure 225. Major plate tectonic features of the West Coast of the Western United States and Mexico.

Provinces of the Coastal Pacific Northwest

The Western Cordilleran Ranges in the Pacific Northwest are subdivided into several physiographic provinces. The major provinces are the Cascades Volcanic Range and the Coast Ranges of the Pacific Borderlands which in Washington include the Olympic Peninsula, Willapa Hills, and the Puget-Willamette Lowlands (a valley between the Cascades and the Coast Ranges)(Figure 226). South of the Columbia River, the Oregon Coast Ranges rise in low, rugged mountains along in a belt between the coastline and the Willamette Valley.

Olympic Peninsula

Olympic National Park encompasses a large portion of the Olympic Peninsula (west of Puget Sound). The Olympic Peninsula is an elevated, erosionally dissected plateau featuring the snow-capped Olympic Mountains. Mt. Olympus, elevation 6,900 feet, is the highest peak in the range and supports small glaciers and perennial ice field despite its low elevation and latitude (Figure 227). Olympic National Park extends to the the Pacific coast, and preserves pristine rugged coastlines and an amazing temperate-latitude coastal rain forest that gets about 12 feet of rain per year (Figures 228 and 229).

In contrast, the cities of Seattle and Tacoma on Puget Sound (in the rainshadow of the Olympic Mountains, although resident might not sense it) averages about 37 inches of rain a year, but it is cloudy (and often raining) about 227 days of the year.
Cascades and Coastal Borelands.
Fig. 226. Cascades and Coastal Borderland Provinces.
Olymic Mountains of the Olympic Peninsula, Washington. Sea stacks along the Olympic Peninsula coastline, Washington. Rainforest of the Olympic National Park, Washington.pic North Cascades Mountains, Washington.
Fig. 227. Olympic Mountains of the Olympic Peninsula, Washington. Fig. 228. Sea stacks along the Olympic Peninsula coastline, Washington. Fig. 229. Rainforest of the Olympic National Park, Washington. Fig. 230. Glaciated peaks in North Cascades National Park, Washington.

Cascades Province

The Cascades Range extends from British Columbia southward into Northern California. The Cascades Provinces are generally subdivided into into the Northern, Central, and Southern provinces, but they all share the same characteristics: a long history of active plate-margin tectonics, intermittent volcanic eruptions, tectonism and earthquakes, and erosion. The Cascades are a belt of "geologically young and active" volcanoes associated with the Cascadia subduction zone along the northern West Coast. The Cascadia subduction zone is not only responsible for the volcanoes in the region, but is a source of great concern for great earthquakes (and tsunamis) that may impact the region. Figure 231 shows the region's major "active" volcanoes—those that have erupted in the past 4,000 years, numerous times!

The modern Cascades volcanoes rise above a landscape that has experiences volcanic activity going back into the Mesozoic Era. Volcanoes in the region have the tendency to build up, explode, collapse, and then rebuild themselves. At the same time, faults in the region are quite active, and erosion is keeping pace, tearing down volcanoes and mountains, and rivers are dumping sediments at sea.
Volcanic eruptions in the Cascades over the past 4,000 years.
Fig. 231.Volcanic eruptions in the Cascades over the past 4,000 years.

Mt. Rainier (in Mt. Rainier National Park, elevation 14,416 feet, and changing) is the highest volcano in the Cascade Rage—it is very scenic feature, but it is perhaps the most dangerous volcano in the United States (Figure 232). The last "significant" eruption of Mt. Rainier occurred in 1894, but the mountain is capable, like other Cascade volcanoes, of producing eruptions and collapse-related floods that could significant change the landscape in the region. The "problem" is that currently about 10,000,000 people live within the "impact zone" if Mt. Rainier were to have a major eruption and collapse that would send sediment-laden floods (lahars) into populated areas around Seattle and Tacoma (along with clouds of ash and gas). It has already happened before... numerous times in the recent geologic past.

Mount St. Helens is "currently" (over the last 4,000 years) the most active volcano in the Cascades Range (Figure 233). The massive eruption of May 18, 1980 was the largest eruption in modern history of the Cascades, but was insignificant compared to other major eruptions that have occurred in pre-historic times. During the eruption about 1/4 cubic mile of volcanic material was blow out of the volcano, most associated by a massive landslide that collapsed a side of the volcano. Geologist have found evidence of eruptions in the region that may have moved hundreds to thousands of times that volume in the past.

Crater Lake National Park in southern Oregon is host to the deepest (and cleanest) freshwater lake in North America (about 2,000 feet deep)(Figure 234). Crater Lake fills the caldera that formed on ancient Mt. Mazama that erupted and collapsed internally to form the crater (caldera) about 9,000 years ago.
Mount Rainier, Washington Mount_St. Helens Crater Lake, Oregon
Fig. 232. Mount Rainier National Park, Washington. Fig. 233. Mount St. Helens National Volcanic Monument. Fig. 234. Crater Lake National Park, Oregon, is the deepest and cleanest lake in the United States.

Cascade Volcanoes in Northern California

The Cascades in northern California are the transition zone to the more ancient volcanic arc preserved as rocks in the Sierra Nevada Range to the south. Mount Shasta is the second highest of the Cascade volcanoes (elevation 14, 179 feet, and changing), but by volume it is the largest. It is a large composite cone, having numerous vents that have contributed to the buildup of the large stratovolcano (Figure 235). Black Butte is a "satellite volcano" on the margins of Mt. Shasta; it is located along Interstate 5 (easily visible) near Weed, California. Black Butte is a "lava dome" volcano about 9,000 years ago (Figure 236).

Lassen Volcano is the southernmost active volcano in the Cascade Range in northern California. Lassen Peak experience a series of eruptions from 1914 to 1917, with the largest happening in 1915. The volcano is now preserved as Lassen Volcanic National Park.

Medicine Lake Volcano is the most expansive volcano in the Cascade Range. It is a large shield volcano that covers a large area in northeastern California. Lava Beds National Monument preserves part of the Medicine Lake Volcano Field (Figures 237 and 238).
Mount Shasta in northern California is the largest of the volcanoes in the Cascades Range. Black Butte, a lava dome volcano along Interstate 5 near Weed, California. Lava Beds National Monument Tule Lake Valley is in a fault bounded graben next to the volcanic Medicine Lake volacanic plateau in northeastern California.
Fig. 235. Mount Shasta in northern California is the largest of the Cascades volcanoes. Fig. 236. Black Butte, a lava dome volcano along Interstate 5 near Weed, California. Fig. 237. Schonchin Butte (a "young" cinder cone) in Lava Beds National Monument. Fig. 238. Tule Lake Valley is in a fault bounded graben in Lava Beds National Monument.

Sierra Nevada Province

The Sierra Nevada Range is the ancestral equivalent of the modern Cascade Range, but it has a significantly different geologic history. The rocks exposed in the core of the Sierra Nevada range are granitic rocks that crystallized in intrusive bodies beneath a volcanic arc system associated with a subduction zone between the Farallon Plate and the North America Plate in Triassic to Cretaceous time. In Late Cretaceous time as the North American Plate rapidly overrode the Farallon Plate, ending subduction in the Sierra Nevada region. By mid Tertiary time, the Sierra Nevada was a low upland region, and rivers flowed from Nevada across the region—carrying the gold mined that was eventually mined from the gravels on the western side of the Sierra Nevada Range during the California Gold Rush.

The Sierra Nevada suddenly began to rise and till westward starting about 4 million years ago. The eastern side of the Sierra has a long series of great normal faults, producing a steep range front that marks the western boundary of the Great Basin. Volcanism followed, producing massive volcanic features associated with Mammoth Mountain volcano and the supervolcano, Long Valley Caldera (20 miles long and 11 miles wide,) that produced a massive eruption 760,000 years ago. The region is sit very geologically active, having both numerous earthquakes and signs of subsurface volcanic activity. Devils Postpile National Monument famous for its columnar jointed lavas exposed in a canyon along the eastern side of the Sierra Nevada Range (Figure240).

Yosemite National Park and Sequoia-Kings Canyon National Park encompass the mountainous terrane in the high country of the Sierra Nevada. The spectacular scenery is a result of the erosion of glaciers that blanketed the high Sierra during the Pleistocene ice ages. Valley glaciers carved the U-shaped, steep rock walled canyons in the parks (Figures 241 to 243).

The eastern Sierra is host to redwood forests that Sequoias (Sequoiadendron giganteum; world’s largest tree, by volume, Figure 244). In comparison, Coast Redwoods (Sequoia sempervirens) are the world’s tallest tree. The eastern Sierra is the only natural habitat for the Sequoias.
Airliner view of the Sierra Nevada over Yosemite National Park, California
Figure 239. Airliner view of the Sierra Nevada over Yosemite National Park, California.
Devils Postpile National Monument
Fig. 240. Devils Postpile National Monument highlights a basalt flow that exhibits spectacular columnar jointing.
Yosemite valley, a glacially carved valley in the heart of the Sierra Nevada Range, California.
Yosemite Falls in glaciated Yosemite Valley in the heart of the California Sierra Nevada Range.
Half Dome, a glacially carved remnant of a granitic intrusion in Yosemite National Park, California.
Giant Sequoia trees in Yosemite National Park.
Fig. 241. Yosemite Valley, a glacially carved valley in the heart of the Sierra Nevada Range, California.
Fig. 242. Yosemite Falls in glaciated Yosemite Valley in the heart of the California Sierra Nevada Range.
Fig. 243. Half Dome, a glacially carved remnant of a granitic intrusion in Yosemite National Park, California.
Fig. 244. Giant Sequoia (redwoods) in Yosemite National Park are the world's largest trees (by size volume).

Great Valley Province

The Great Valley is low low plains region on the west side of the Sierra Nevada Range and east of the Coast Ranges in central and northern California. It is divided into two parts, the Sacramento Valley is north of the Sacramento River, and the San Joachin Valley extends southward from the Sacramento River to the Tehachapi Mountains near Bakersfield near its southern end (Figure 245). Before the end of subduction and the formation of the San Andreas Fault, the Great Valley was part of the continental shelf and foreland basin. A thick sequence of marine sedimentary deposits accumulated in the foreland basin and is called the Great Valley Sequence (Figure 246). As the San Andreas Fault system developed, the Coast Ranges gradually formed, and the Great Valley deposits transitioned from marginal marine to terrestrial environment.

The Great Valley was flooded by large lakes during the Ice Ages, and parts of the valley were flooded by shallow lakes up until historic times. Tulare Lake was the largest freshwater lake west of the Mississippi River until the Kern River was diverted for agricultural irrigation and municipal water uses. The Great Valley is very prone to flooding... and droughts. Few regions of the world have undergone as much modification of the natural drainage system. With ample sunshine, warm climate year round, and when water is available, the Great Valley is one of the most productive agricultural regions of the world. The Sacramento Valley was host to the start of Gold Rush of 1849 that started a major human migration to California.

The southern San Joachin Valley has historically been one of the largest oil producing basins in California (Figure 247). Oil production is mostly from Miocene and older age marine sediments with oil reservoirs located along the crests and margins of great anticlines along the basin. Tectonic folding and faulting along the San Andreas Fault and associated faults are actively pushing up the Coast Ranges. Near the south end of the Great Valley is Carrizo Plain National Monument. Because of the very arid climate, the park preserves exception geologic features associated with motion and changes associated with great earthquakes on the San Andreas Fault (Figure 248).

Interstate 5 runs north-south along the western side of the Great Valley between Bakersfield and Stockton. Along the interstate, the foothills of the coast ranges rise to the west in a series of hills and ridges include, from south to north, the Kettleman Hills, Tume Hills, and Panoche Hills. These rolling hills, badlands, and cattle rangelands are a stark contrast to the flat agricultural lands east of the interstate. Gently to steeply dipping layers of the Great Valley Sequence are well exposed in these areas (Figure 249).
San Andreas Fault System in California and the Salinian Basement rocks of the California Coast Ranges
Fig. 245. Map showing the relationship of the Sierra Nevada, Great Valley, and Coast Ranges relative to the San Andreas Fault system. Rocks on the west side of the San Andreas Fault have moved (and are moving) northward relative to rocks east of the fault.
Generalized cross section of central California.
Fig. 246. Generalized cross section through central California.
One of many oil fields in the San Joachin Basin near Bakersfield, California. Fig. 247. One of many oil fields in the San Joachin Basin near Bakersfield, California. Oil production has been going on since the 1920s in the region.
Soda Lake episodically floods a shallow basin next to the San Andreas Fault in Carrizo Plain National Monument.
Fig. 248. Soda Lake episodically floods a shallow basin next to the San Andreas Fault in Carrizo Plain National Monument.
Tume Hills on the west side of the Great Valley, Central California.
Fig. 249. Tertiary-age sediments of the Great Valley Sequence is exposed in the Tume Hills on the west side of the Great Valley.

Coast Ranges Provinces

The Coast Ranges of Oregon and California are rugged mountainous country with complex geology. Most of the region is new land that has formed since Mesozoic time by the tectonic actions involving subduction and accretion of small landmasses and pieces of ocean crust that were pushed onto the continental margin rather than being subducted. The Coast Ranges are subdivided into sections including, from north to south, the Oregon Coast Ranges, the Kamath Mountains (straddling the Oregon California border), the Northern Coast Ranges (extends southward from Crescent City, California the Northern San Francisco Bay Area), the Southern Coast Ranges (between San Francisco and Santa Barbara), the Transverse Ranges (between Santa Barbara and Los Angeles), and the Peninsular Ranges that extend from Los Angeles to the southern tip of Baja California. South of Cape Mendicino, the San Andreas Fault and other regional faults are important to the geography and natural history of the Coast Ranges (Figure 250).

Oregon Coast Ranges

Oregon Coast Ranges
extend from the Columbia River south into northern California where they transition into the Klamath Mountains and the Northern Coast Ranges of California. North of Cape Mendicino near Cape Mendicino the Cascadia Subduction Zone is actively contributing materials that are being pushed up into the ranges. In Oregon the Coast Ranges are about 30 to 60 miles wide and have an average elevation of about 1,500 feet. The rocks exposed in the Oregon Coast ranges are mostly Tertiary age fore-arc basin deposits.
Physiographic provinces of California.
Fig. 250. Physiographic provinces and geology of California.

Klamath Mountains

The Klamath Mountains straddle the Oregon-California border and are both geologically older and distinct, and higher than the other Coast Ranges north and south (Figure 251). The region hosts coniferous forests features and higher mountain ranges than the other Coast Ranges including the Trinity Alps, Trinity Mountains, Siskiyou Mountains, and Marble Mountains, with higher peaks rising above 8,000 to 9,000 feet. With the higher elevations, the region receives higher precipitation rates, mostly in the winter months with high snow fall rates. The Klamath Mountains are composed of “terranes”—slivers of ocean crust, island masses, and blocks of continental crust. Between 260 million (Late Permian) and 190 million (Early Jurassic) years ago a succession of eight terranes were rafted in by the Farallon Plate and accreted onto the continental margin. These terranes were metamorphosed and intruded by magmatic plutons, creating a very diverse suite of rocks with marble, serpentinite, and gabbroic to granitic intrusive igneous being most abundant. One of the marble-bearing terranes is host to Oregon Caves National Monument and Preserve.
Klamath Mountains.
Fig. 251. The Klamath Mountains straddle the Oregon-California border and are higher and older than the other Coast Ranges.

Northern Coast Ranges of California

The Northern Coast Ranges run north-to-south, generally parallel to the coast. U.S. Highway 101 (the Coast Highway) runs along valleys between Inner and Outer ranges, separated by the river valleys of the Eel River to the north, and the Russian River to the south. The outer ranges run to the coast and are wetter and are mostly forested with Coast Redwoods, Ponderosa Pine, and deciduous forests (Redwoods National Park is along the coast between Crescent City and Arcada, California). The inner ranges border the Great Valley are dryer with mixed evergreen and oak woodlands, and chaparral. Bedrock in the North Coast Ranges are mostly Jurassic, Cretaceous and Tertiary rocks derived from terranes and ocean crust scraped from the Farallon Plate before the San Andreas Fault propagated across the region north of San Francisco starting about 12 million years ago (Late Miocene). The Northern Coast Ranges are mostly below 2,000 feet, but some peaks are higher. Cobb Mountain, elevation 4,724, is the highest.

The Northern Coast Ranges are host to two volcanic fields. The Sonoma Volcanic Field is located at the northern end of the Napa and Sonoma Valleys and was most active during Pliocene time. Its residual heat is illustrated by the Calistoga Geyser, often called the “Old Faithful Geyser of California” (Figure 252). The Clear Lake Volcanic Field is about 90 miles of San Francisco is has been active through Pleistocene time with the most recent volcanism about 11,000 years ago. The Clear Lake Volcanic Field is now host to the world’s most productive geothermal energy power plants, supplying enough electricity for about 850,000 homes in the region.
Calistoga Geyser, "Old Faithful Geyser of California" in northern Napa Valley.
Fig. 252
. Calistoga Geyser, "Old Faithful Geyser of California" in northern Napa Valley.
A "marine layer" (fog bank) settled in along the Coast Range in Humboldt County, northern California. The Mendicino Range and Mayacama Mountains are outer ranges that extend south into Sonoma and Napa Counties. Napa Valley Mt. Tamalpias is the highest peak in the Northern Coast Ranges, and overlooks the San Francisco Bay Area.
Fig. 253. A "marine layer" (fog bank) settled in in Northern Coast Range in Humboldt County, California. Fig. 254.The Mendicino Range and Mayacama Mountains are outer ranges that extend south into Sonoma County. Fig. 255. Mount Hood, elevation 2,750 feet, rises above Napa Valley, the premiere wine growing region. Fig. 256. Mt. Tamalpais, southernmost peak in the Northern Coast Ranges, overlooks San Francisco Bay.

San Francisco Bay Region

Despite hosting more than 7 million people in 9 counties and over 100 incorporated cities, most of the land is set aside as open space preserves and parklands. Most of the urban development is in the lowlands surrounding San Francisco Bay. Rocks in the region are mostly Jurassic, Cretaceous, and Tertiary age, consisting of belts of rock associated with fault-bounded terranes (Figure 257). Hazards associated with fire, landslides, and earthquake faults make building in the mountainous areas largely unpractical. The San Andreas Fault, Hayward Fault, Calaveras Fault, and San Gregorio Faults are major earthquake faults that have produced significant earthquakes in the region. San Francisco Bay floods that ancestral Sacramento River Valley where it carved its Golden Gate canyon through the Coast Ranges when sea level was almost 400 feet lower during the Pleistocene ice ages. The Golden Gate Bridge spans the bay between San Francisco and the Marin Headlands in Marin County (Figure 258). Golden Gate National Recreation Area encompasses parklands on both sides of the Golden Gate. North of the Bay are Muir Woods National Monument, a redwoods preserve, and Point Reyes National Seashore (Figure 259). Point Reyes Peninsula is a terrane on the west side of the San Andreas Fault and are part of the Salinian Block. The Salinian Block is composed of continental crustal rocks, mostly granite and marble basement rocks overlain by younger sedimentary formations. The Salinian Block shares its origin with the rocks in the Sierra Nevada Range—both were part of the ancestral Cordilleran volcanic arc that developed in the Mesozoic Era. Bedrock east of the Salinian Block consist of the Franciscan Formation—the formation is composed of a mix of rocks derived from ocean crust and deep ocean sediments derived from the ancestral Farallon Plate. Fault-bounded blocks of both Salinian and Franciscan materials have moved northward along fault systems along the California coast, in some cases by hundreds of miles since their time origin (see Figure 245).
General geologic map of the San Francisco Bay Area.
Fig. 257
. Map of the San Francisco Bay region showing geology and major faults.
Golden Gate Bridge from the Marin Headlands side of San Francisco Bay.
Headlands and Coves at Point Reyes National Seashore, northern California.
Montara Mountain, San Francisco Peninsula, California.
Pigeon Point, San Francisco Peninsula, California.
Fig. 258.The Golden Gate Bridge crosses the narrows of San Francisco Harbor between the highlands of San Francisco and the Marin Headlands Fig. 259.Headlands and Coves at Point Reyes National Seashore. Point Reyes is a part of the Salinian Block on the west side of the San Andreas Fault. Fig. 260. Montara Mountain on the San Francisco Peninsula coast in San Mateo County is composed of a large block of Salinian granite. Fig. 261. Pigeon Point along the coast of San Francisco Peninsula is part of a Sur Series terrane located on the west side of the San Gregorio Fault.

Santa Cruz Mountains and Santa Clara Valley

The north end of the Santa Cruz Mountains begins where the San Andreas Fault comes onshore near Daly City. Montara Mountain at the north end of the range is a massive exposure of Salinian granitic basement on the west side of the fault (Figure 260). The Santa Cruz Mountains stretch for 80 miles south to the Pajaro River Gap near Watsonville. The Santa Cruz Mountains and started rising above sea level about 4 million years ago, pushed up by compression created by a large bend in the San Andreas Fault. The east side of the Salinian Block is the San Andreas Fault; the west side of the block is bounded by the San Gregorio Fault—the fault comes onshore near Half Moon Bay and again at Pigeon Point (Figure 261). The city of Santa Cruz is developed on the elevated marine terraces on the southern flank of the mountains. The Santa Cruz Mountains on the San Francisco Peninsula are mostly preserved as parklands, open space preserves, watershed for regional cities and several Coast Redwood preserves (Figure 262).

The Santa Clara Valley runs roughly south and east of southern San Francisco Bay, entrenched between the Santa Cruz Mountains and the Diablo Range to the east. San Jose (a large part of “Silicon Valley”) is situated at the north end of the valley. San Jose was started, in part, with commerce supporting the mining of mercury (supplying mercury need for the California Gold Rush). The mercury comes from mineralized veins associated with serpentinite in the New Almaden Mining District in the eastern foothills of the Santa Cruz Mountains. Mt. Umunhum (elevation 3,486 feet;1,063 m) and Loma Prieta (elevation 3,786 feet; 1,154 m) are high point in the range along the Sierra Azul Ridge that runs along the east side of the San Andreas Fault (Figures 263 and 264). Rocks of several terranes and different ages make up the Franciscan Basement rock throughout the Santa Clara Valley. South of the Pajaro Gap (canyon of the Pajaro River), the San Andreas Fault runs down the east side of the Gabilan Range to where it converges with the Calaveras Fault south of Hollister at the southern end of the valley. Mission San Juan Bautista was built near Pajaro Gap on the fault scarp of the San Andreas Fault—it became the first “earthquake-engineered” building in the United States (Figure 265). To the south, the San Andreas Fault then roughly parallels the canyons and valleys of San Benito River south between the Diablo Range (on the east) and the Gavilan Range (to the west).
Giant Redwoods in Big Basin State Park, California.
Calero County Park with Mt. Umunhum and Sierra Azul Ridge in the distance.
Loma Prieta and the Santa Clara Valley near Morgan Hill, California.
Mission San Juan Bautista and historic El Camino Real on the San Andreas Fault Scarp.
Fig. 262. A forest of giant redwoods are preserved in Big Basin State Park in the Santa Cruz Mountains between San Jose and Santa Cruz. Fig. 263. Manzanita grows on serpentinite in the foothills of the Santa Cruz Mountains east of Mt. Umunhum and Sierra Azul Ridge (in the distance) Fig. 264. Santa Clara Valley with El Toro [Peak] near Morgan Hill, California and Loma Prieta Peak and Sierra Azul Ridge in the distance. Fig. 265. The historic El Camino Real runs along the rupture scarp of the San Andreas Fault next to Mission San Juan Bautista.

Monterey Bay Region

Monterey Bay is at arc-shaped bay at the head of Monterey Canyon, a 10,000 foot deep submarine canyon that descends into abyssal depths offshore. The canyon is at the mouths of the Pajaro and Salinas Rivers between the cities of Santa Cruz and Monterey (Figure 266). The Santa Lucia Range runs roughly north-south along the coast south of Monterey; its steep western slope is called the Big Sur (Figure267). The San Gregorio-Hosgri Fault runs along the coast offshore of the Big Sur. The Salinas Valley is bordered by the Santa Lucia Range on the west and Gabilan Range on the east. Arroyo Seco (meaning "dry wash") drains from a canyon the eastern side of the Santa Lucia Range into the broad valley of the Salinas River Valley (Figure 268). Junipero Serra Peak, elevation 5,857 feet, is the highest in the high peaks portion of the Santa Lucia Range.

Fremont Peak
(elevation 3,455 feet) was named after John C. Fremont, the military explorer who planted a US flag on the peak in 1848 before fleeing to Oregon to escape from a Mexican army. Fremont Peak is the highest peak at the north end of the Gavilan Range (Figure 269). The top of the mountain is a great block of marble of late Paleozoic age. Both the Santa Lucia and Gabilan Ranges are part of the Salinian Block on the east side of the San Andreas Fault. Pinnacles National Park is at the south end of the Gabilan Range (Figure 270). The Pinnacles are the eroded remnant of half of a volcano that formed about 23 million years ago on the San Andreas Fault. The other half of the Pinnacles formation is preserved a the Neenach Formation 195 miles south in the western Tehachapi Mountains.
Shaded relief map showing bathmetry and topography of the Monterey Bay region.
Fig. 266. Shaded relief map showing bathymetry and topography of mountain ranges and valleys the greater Monterey Bay region.
Sea cliffs along the Big Sur, the Santa Lucia Range, central California
Arroyo Seco Canyon in the Santa Lucia Range, Monterey County, CA.
Fremont Peak overlooking the Salinas Valley, Monterey County, California.
Pinnacles National Park preserves half of a volcano, the other half is 195 miles south near Tehachapi, California.

Fig. 267. Big Sur is the rugged coast on the west side of the Santa Lucia Range south of Monterey Bay.

Fig. 268. Arroyo Seco Canyon in the Santa Lucia Range displays several well preserved river terraces. Fig. 269. Salinian Block marble crops out on Fremont Peak overlooking the Salinas Valley, Monterey County, California. Fig. 270. Pinnacles National Park preserves half of a volcano torn apart my movement on the San Andreas Fault.
View looking south along the crest of the Gavilan Range showing the anticlinal structure of the range.
Fig. 271. View looking south along the crest of the Gabilan Range showing the anticline structure of Salinian Basement exposed in the core of the range.

The Diablo Range

The Diablo Range is the belt of mountains on the east side of the Santa Clara Valley and San Benito River Valley to the south. Geologically, the Diablo Range is on the east side of the Calaveras Fault and San Andreas Fault at its southern end. The range extends south from the Carquinez Straight in the East Bay and Sacramento River Delta region. The range runs south along the west side of the Great Valley to the Carrizo Plain. Mt. Diablo (elevation 3,889 feet; 1,185 m) is a high peak at the north end of the range. Mount Hamilton (elevation 4,260 feet; 1,300 m) is near San Jose is home of the historic Lick Observatory. San Benito Mountain (elevation 5,241 feet ; 1,597 m) is the highest peak in the southern end of the Diablo Range. Most of the rest of the range is within elevations of 1,500 to 3,000 feet. Bedrock in the Diablo Range consists of Franciscan Basement rocks (with serpentinite) and where present, overlain by the Great Valley Sequence and younger Tertiary sedimentary rocks (Figure 272). Physical landscape features associated with San Andreas Fault system stand out along the surface ruptures (Figure 273). The town of Parkfield (population of a couple dozen) is one of several towns to claim it is the "Earthquake Capitol of the World" (Figures 274 and 275).
Franciscan basement with serpentinite overlain by Great Valley Sequence in the Diablo Range south of Pinnacles National Park. Diablo Range Sag Pond along the San Andreas Fault between Coaling and King City, CA. Parkfield, Earthquake Capital of the World. This bridge in Parkfield, California displays offset warping by motion on the San Andreas Fault.
Fig. 272. Franciscan basement with serpentinite overlain by Great Valley Sequence in the Diablo Range south of Pinnacles National Park. Fig. 273. Sag Pond next to fault scarp along the San Andreas Fault in the Diablo Range between Coaling and King City, CA. Fig. 274. Parkfield, California, claims to Earthquake Capital of the World. It experiences a major earthquake about every 20 years. Fig. 275. This bridge over Cholame Creek in Parkfield, California displays offset warping by motion because it crosses the San Andreas Fault.

Transverse Ranges

The Transverse Ranges are generally east-to-west trending coast ranges between San Luis Obispo and Los Angeles. The Transverse Ranges are the highest of the coast ranges, and consist of about a dozen named mountain ranges. The Transverse Ranges are fairly complex because of if the dynamic interaction of the San Andreas Fault system with the east-west trend Garlock Fault. The largest historic earthquake in California was the Tejon Pass Earthquake of 1857 (estimated M7.9) happened near the intersection of the two great fault systems.

At the north western end are the Nine Sisters, a volcanic field consisting of a series of 13 volcanic plugs and intrusive bodies, including Morro Rock at its western end (Figure 276). The volcanic features formed about 23 to 28 million years ago (Late Oligocene to Early Miocene). Strands of the San Gregorio-Hosgri Fault system comes onshore at Morro Bay and near Avila Beach in San Luis Obispo County.

The Santa Ynes Mountains are an east-west trending mountain range that rise along the coast in Santa Barbara and Ventura Counties (contributing to the scenery along Highway 101 west of Los Angeles). The Santa Monica Mountains on the southwest side of Los Angeles are the southernmost of the Transverse Ranges. Channel Islands National Park encompasses four islands south of the Santa Barbara (Figures 277 and 278). The islands follow a geologic trend that continues west from the Santa Monica Mountains. Los Padres National Forest and Angeles National Forest encompasses the forested highland ranges inland from the coast.

The San Gabriel Mountains are on the north of the Los Angeles Basin. Mount San Antonio, elevation 10,064 (3,068 m) is the highest peak. The San Bernardino Mountains are at the eastern end of the Transverse Ranges—they are also the highest of the Coast Ranges. San Gorgonio Peak is the highest peak in the range, elevation 11,501 feet (Figure 279). The San Andreas Fault runs along the north side of the San Gabriel and San Bernardino Mountains.
Morro Rock is an eroded remnant of a volcanic plug, central California coast.
Sea cliff with a marine terrace on Santa Cruz Island, the largest of the Channel Islands near Santa Barbara, CA. Sea Cliff on Santa Cruz Island, one of the Channel Islands, California. San Gorgornio is the highest peak in the Transverse Ranges, elevation
Fig. 276. Morro Rock is one of the Nine Sisters, a series of eroded volcanic plug along the central California coast in San Luis Obispo County, CA. Fig. 277. Sea cliff with a marine terrace on Santa Cruz Island, the largest of the Channel Islands near Santa Barbara, CA. Fig. 278. Sea Cliff of Miocene-age Monterey Formation on Santa Cruz Island, one of the Channel Islands, California. Fig. 279. San Gorgonio Peak in the San Bernardino Mountains is the highest peak in the Transverse Ranges, elevation 11,501 feet.

Peninsular Ranges

The Peninsular Ranges are a group of Coast Range mountains that trend north-to-south and run from near Los Angeles southward into Mexico’s Baja Peninsula (Figure 280). Interstate 10 between Los Angeles and Palm Springs runs through San Gorgonio Pass, a valley that divides the Transverse Ranges to the north from the Peninsular Ranges to the south. San Jacinto Peak, 10,834 ft (3,302 m), is the highest peak in the San Jacinto Mountains and highest in the Peninsular Ranges. San Jacinto Peak overlooks Palm Springs and San Gorgonio Pass (Figure 281). Rocks exposed in the Peninsular Ranges are mostly Mesozoic-age granites that have intruded older, partially metamorphosed sedimentary and volcanic rocks. The rocks that make up the Peninsular Ranges are part of the Salinian Block, a long linear section of crust that was originally attached to the North American Plate, but became detached and has gradually moved northward along the west side of the San Andreas Fault. The Peninsular Ranges have been rising as new ocean crust is forming along spreading centers underneath the Gulf of California and the Colorado Desert region (see Figure 225). The coast mountains are mostly chaparral with oak woodlands, with mixed conifers in higher elevations (Figures 282 and 283). San Diego County has 24 peaks over 5,000 feet; Hot Springs Mountain, elevation 6,533 feet is the highest.
Peninsular Ranges are the core of the Baja Peninsula between Los Angeles and Cabo San Lucas, Mexico.
Fig. 280. Peninsular Ranges are the core of the Baja Peninsula between Los Angeles and Cabo San Lucas, Mexico.
San Jacinto Peak,
Peninsula Ranges in San Diego County. View from Mount Palomar, a high ridge in the Peninsular Range in San Diego County.
Fig. 281. San Jacinto Peak, 10,834 ft, near Palm Springs, is the highest peak in the Peninsular Ranges. Fig. 282. Peninsula Ranges in northern San Diego County. Lake Hodges Reservoir fills the valley of the San Dieguito River, one of the principle streams draining the highlands of the northern Peninsular Ranges. Fig. 283. View from Mount Palomar, a high ridge in the Peninsular Ranges in northern San Diego County.

Coastal Southern California

Southern California is notoriously famous for having numerous active Earthquake faults, both onshore and offshore (Figure 284). Southern California has submerged borderlands offshore. The Channel Islands (to the north) and San Clemente Island, Catalina Island, and San Nicolas Island are exposed tops of several submerged seamount ranges off the coast. Santa Catalina Island is a block of ocean crust of the ancient Farallon Plate that escaped subduction and accretion onto the continent (Figure 285).

The coastline of San Diego County is highlighted by a series of step-like marine terraces carved by wave erosion as sea level has risen and fallen as the coast is slowly rising. Step-like terraces can be seen along the coast from Los Angeles to San Diego Bay (Figure 286). The west side of the Peninsular Ranges are slowly rising. Wave-cut cliffs along the coast exposed sedimentary rock formations that originally were deposited as sediments in coastal marine environments. Cabrillo National Monument is on Point Loma,a fault-bounded highland peninsula overlooking San Diego Bay (Figures 287 and 288).
Southern California, bathymetry, topography, and faults. Fig. 284. Southern California, bathymetry, topography, and faults.
2000 foot sea cliffs on Catalina Island, one of the Channel Islands off the coast of southern California. Tertiary rock formation exposed in sea cliffs at Del Mar Dog Beach, Solano Beach, California. Cretaceous rocks crop out along sea cliffs at Cabillo National Monument, San Diego, California San Diego Bay.
Fig. 285. 2000 foot sea cliffs on Santa Catalina Island, one of the Channel Islands located off the coast of southern California. Fig. 286. Tertiary rock formations exposed in sea cliffs under elevated marine terrace deposits at Del Mar Dog Beach. Fig. 287. Cretaceous rocks crop out along sea cliffs at Cabillo National Monument, San Diego, California. Fig. 288. View looking east from the highlands on Point Loma overlooking San Diego Bay and Coronado Island.

Alaska and Hawaii

Alaska encompasses an expansive region of the Western Cordillera (Figure 289). Belts of mountain range border both sides of a central lowlands and plateaus region. The southeastern Alaska Panhandle consists of an archipelago of islands and coast ranges. The mountainous coastline bordering the Gulf of Alaska has glaciers and fjords (submerged glaciated valleys). Cool climates and high precipitation are responsible for numerous ice caps and alpine glaciers. Some of the glaciers reach the ocean, forming tidewater glaciers, such as at Glacier Bay National Park and Kenai Fjords National Park (Figure 290 and 291).

The Pacific Plate is colliding directly with the North American Plate. The results include the highest mountain ranges and most active volcanoes on the continental United States. Denali National Park hosts the highest peak in North America (Figure 292). Wrangell-St. Elias National Park and Preserve encompasses a large region extending from the coast into the Alaska Range and is host to the Wrangell Volcanic Field (Figure 293). The Aleutian Range is volcanic arc that extends from near Anchorage to the Aleutian Island Chain which extends about 1,200 mile westward from the Alaska Peninsula toward the Kamchatka Peninsula in Russia and divides the Pacific Ocean from the Bering Sea. The interior of Alaska is a series of low mountain ranges, plateaus and lowlands drained by the Yukon River. The northern Alaskan Brooks Range is a more ancient mountain range that is bonded on the north by the" North Slope" Arctic Coastal Plain and continental margin basin that is host to Alaska's major oil fields.
Map of physiographic features in Alaska.
Fig. 289. Map of physiographic features in Alaska. The Aleutian Trench runs along the Pacific margin of Alaska and Aleutian Islands and is an active convergent plate boundary.
Satellite view of tidewater glaciers in Glacier Bay National Park. Kenai Fjords National Park is on the Gulf of Alaska near Seward, Alaska. Denali, Mt. Drum,
Fig. 290. Satellite view ice-capped mountains and tidewater glaciers in Glacier Bay National Park. Fig. 291. Kenai Fjords National Park has glaciers and submerged valleys along the Gulf of Alaska near Seward, Alaska. Fig. 292. Denali, elevation, 20,301 feet, is the highest mountain in North America—in Denali National Park. Fig. 293. Mt. Drum is a Pleistocene volcano in Wrangell-St. Elias National Park and Preserve, Alaska.

Hawaii

As the Pacific Plate has been moving westward over the Hawaiian Hotspot, it has produced the Emperor Seamount Chain. The Hawaiian Islands are at the eastern end of the chain, and are the youngest (Figure 294). Volcanoes on the Big Island (Hawaii) and Maui have erupted in historic times. Mauna Loa is a massive shield volcano on Hawaii that rises from ocean depths to its peak of 13,678 feet, making it is the tallest mountain on Earth (Figure 295). Hawaii's volcanoes are the most active on the planet. Big Island eruptions have been proceeding nearly continuously since 1983. The eruptions are generally gentle (not explosive like volcanic arc eruptions in the Cascades or Alaska), the basaltic lava is extremely hot, and therefore flows long distances, often spilling into the ocean. The lava builds up shield-shaped volcanic cones (Figures 296 to 298). When the volcanoes stop erupting (after they move off the hotspot magma source) erosion takes over, wave erosion carves massive sea cliffs on the windward side of the islands (such as the Na'Pali Coast on Kawaii, Figure 299). Mt. Waialeale on Kauai gets about 460 inches of rain a year, making it the wettest place in the United States.
Map of Hawaii showing topography and bathymetry.
Fig. 294. Map of Hawaii showing topography and bathymetry. The islands are on the east end of the Emperor Seamount Chain. The Hawaiian Hot Spot is underneath the Big Island.
Mauna Loa is a massive shield volcano on Hawaii and from ocean depthts to its peak of
Fig. 295. Mauna Loa is a massive shield volcano on Hawaii and from ocean depths to its peak of 13,678 feet is the tallest mountain on Earth. The summit is in Hawaii Volcanoes National Park.
Pu'u'o'o volcano erupting on the flank of Kilauea Volcano in Hawaii Volcanoes National Park.  Volcano Halualia Volcano rises above the Kona Coast on the Big Island of Hawaii. Haleakala volcano on Maui across Alenuhaha Channel.  Na'Pali Coast on the island of Kawaii.
Fig. 296. Pu'u'o'o Volcano erupting on the flank of Kilauea Volcano in Hawaii Volcanoes National Park. Fig. 297. Halualai Volcano, one of the five big volcanoes on the Big Island, rises above the Kona Coast. Fig. 298. Haleakala volcano rises above the clouds across Alenuhaha Channel between the islands of Maui from Hawaii. Fig. 299. The Na'Pali Coast on the island of Kawaii has high sea cliffs and deep canyons.

http://gotbooks.miracosta.edu/geology/physiography.html
10/21/2016