Elsinore Fault Zone

Overview of the Elsinore Fault Zone

• The Chino Fault section and Whittier Fault section are two northern fault strands that merge into the Elsinore Fault zone near Corona, CA.
• The Glen Ivy Fault section extends about 29 miles (46 km) between Corona and Lake Elsinore.
• The Temecula section extends about 39 miles (62 km) from Lake Elsinore southward through Temecula to Pauma (near the northern San Diego County line).
• The Julian section extends about 49 miles (79 km) from Pauma (near Palomar Mountain) past Lake Henshaw, Julian, and into the Anza Borrego State Park area.
• The Coyote Mountain section starts near Agua Caliente State Park and extends south about 20 miles (33 km) to the vicinity of Ocotillo, CA near Interstate 8.
• Laguna Salada Fault is a southern extension of the Elsinore Fault Zone that extends south 38 miles (61 km) into northern Baja California.

Earthquake History and Information

• The probable magnitude of a major earthquake along the Elsinore fault zone could be in the range of magnitude 6.5 to 7.5 (Mw).
• The estimates slip rate for the fault is reported as roughly 4.0 mm/year.
• The probable recurrence interval between major ruptures along the fault zone is roughly estimated between 250 and 600 years. These estimates vary from studies along different fault strands and location along the fault zone).
• The most recent surface rupture in the northern and central sections occur in the 18th century, surface rupture occur at the southern end in 2010.
• The recurrence interval given above suggests slip of 1.25 to 1.5 meters per surface-rupturing event.

Map For Studying the Elsinore Fault Zone

USGS Quaternary Faults Data in Google Earth (Virtual Elsinore Fault Field Trip)

Geologic Setting

Northern Sections of the Elsinore Fault Zone

Central Sections of the Elsinore Fault Zone

Southern Sections of the Elsinore Fault Zone

Geomorphic Expression Of Faults

Elsinore Fault Zone - Study Areas & Maps

There are 21 study areas along the Elsinore Fault Zone presented below. Each section includes a geographic map (with stop localities shown as red dots), a satellite map (with fault lines added), and a geologic map (various sources listed in the Resources Section below). The fault lines shown on the maps and satellite images presented below were derive from the Quaternary Folds and Faults Database of the United States (QFFDUS). The original images derived from the database have been slightly modified and enhanced to bring out clarity of relief and landscape features, and identifying labels have been added to help navigate to features and locations to be potentially investigated. QFFDUS IDs are added to provide access to more detailed technical reports listed for each of the seven sections of the Elsinore Fault Zone being investigated here. Note that names of faults and features may have changed over time in the literature going back over a century.

The purpose of this investigation/website: This website is being prepared in anticipation of camping field trips for students in classes at Miracosta Community College (and elsewhere). Students will be using this website to learn to recognize fault-related landscape features, to learn to navigate using maps and imagery to potential investigation sites. To cover the entire fault zone adequately would take several days on field trips, but it can easily be followed "virtually" using Google Earth (discussed below).

Corona CA: Where the Whittier Fault, Chino Fault, and Glen Ivy Fault Sections Converge

In the vicinity of CA Highway 91 in Corona, CA, the Elsinore Fault Zone splits into three sections in a left-tilted "Y" fashion.

To the northwest is the Whittier section (also known as the Whittier Fault) runs along the southwest-facing mountain front of the Puenta Hills (or Chino Hills). It continues northwest from the Corona area to the Whittier region of Los Angeles (a distance of about 20 miles). At the northwest end of the Puente Hills, the Workman Hill and Whittier Heights faults appear to split from the Whittier Fault and disappear under alluvial cover in the LA basin region.

To the north is the Chino section (also known as the Chino Fault) that runs along the southwest-facing mountain front of the Puenta Hills (or Chino Hills). The Chino section follows CA Highway 71 north about 5 miles before petering out in the Los Serenos Country Club area. To the north the fault probably continues as the Central Avenue Fault northward into the Chino/Pomona region of Los Angeles (a distance of about 12 miles). (Older reports call the Chino Fault the Central Avenue Fault.)

South of CA Highway 91 in Corona, the Chino Fault and Whittier Faults converge and continues south as the Glen Ivy section of the Elsinore Fault Zone. The fault zone follows the mountain front along the southwest side of Corona, CA. The Glen Iva section runs along the Interstate 15 corridor between Corona and Lake Elsinore (a distance of about 18 miles).

Study Area 1 - Whittier Fault and Chino Fault Sections

Whittier Fault (Modified from SCEDC summary)

• TYPE OF FAULT MOTION: The Whittier Fault displays right-lateral strike-slip with some reverse slip.
• FAULT ORIENTATION: The average strike is N70°W; the fault plane dips to northeast at low-angle to near vertical (90°). The right-lateral displacement of about 40:1 ratio (D:R) as indicated by Rockwell, Gath and Gonzalez (1992).
• LENGTH: about 16 miles (36 km)
• LOCATION: Orange County and Los Angeles County; It extends along the west side of the Puente Hills (Chino Hills), from Whittier in the northwest to the Santa Ana River on the southeast.
• NEAREST COMMUNITIES: Yorba Linda, Hacienda Heights, Whittier
• MOST RECENT SURFACE RUPTURE: Holocene. Last event occurred between 1400 and 2200 yr BP with a minimum of 1.9 m of dextral offset (Patterson and Rockwell, 1993; Working Group on California Earthquake Probabilities, 1995).
• SLIP RATE: between 2.5 and 3.0 mm/yr
• INTERVAL BETWEEN MAJOR RUPTURES: unknown
• PROBABLE MAGNITUDES: Mw6.0 - 7.2
• GEOMORPHIC EXPRESSION: Large dextral stream deflections (>1 km) document Quaternary displacement; smaller stream offsets, side-hill benches, linear drainages express Holocene activity.
• OTHER NOTES:  The Whittier Fault was named by English (1926). QFFDUS ID: Elsinore Fault Zone, Whittier section 126a.

Chino Fault (Modified from SCEDC summary)

• TYPE OF FAULT MOTION: right-reverse (oblique slip)
• ORIENTATION: Average strike: N42°W; the dip of this fault plane is to the southwest (50–67° W).
• LENGTH: 13 miles (21 km)
• LOCATION: Riverside and San Bernardino Counties; the fault runs along the southwest flank of the the Chino/Puente Hills and merges with other faults in the northern end of Glen Ivy section of the Elsinore Fault Zone near Corona.
• NEAREST COMMUNITIES: Corona, Chino
• MOST RECENT SURFACE RUPTURE: Late Quaternary to early Holocene.
• INTERVAL BETWEEN MAJOR RUPTURES: unknown
• PROBABLE MAGNITUDES: Mw6.0 - 7.0
• RECENT EARTHQUAKE: The Mw 5.4 Chino Hills earthquake occurred in the area on 29 July, 2008.
• SLIP RATE: between 1 and 5 mm/yr
• GEOMORPHIC EXPRESSION: Saddles, deflected drainages, linear drainage, modified scarps.
• OTHER NOTES: The Chino Fault was named by English (1926). QFFDUS ID: Elsinore Fault Zone, Chino section 126b.

Chino Fault Section (northern part)

If you plan to check out the Chino Hill Fault it would be easiest to start the field trip by going first to the Chino Hills State Park area, then work your way south before going to the Whittier Hills area on Green Valley Road (discussed below). The problem with accessing the Chino Hills and Whittier Fault sections is that most of the associated is inaccessible (on fenced-off or private land with "no trespassing" signs).

Chino Hills State Park: To get to the Chino Hills SP, take Highway 71 to Exit 7 (Central Ave./Soquel Canyon Rd). Follow Soquel Canyon Road west about 1 mile and turn left on Elinvar Drive. In less than 1/4 mile the road curves to the right (becoming Sapphire Rd). The North Entrance of Chino Hills State Park is on the right (Figure 1-6). The park requires an entrance fee and there are campground facilities available (make reservations online). The park road follows Bane Canyon, a straight canyon that probably formed along a subsidiary parallel fault strand of the Chino Fault (Figure 1-7). Note that the grassy hills cover the soft, easily eroding hills of soft Pliocene-age sediments that underlie the Chino Hills area. Note that the Bane Canyon Road that goes into the park is one lane (with pull offs with "no parking" signs) until you get to the park entrance pay station. Watch out for bikes on this narrow road.

Note that you don't have to go into the park to see the trace of the Chino Fault. Park on Sapphire Road just east of the Chino Hills State Park entrance sign. The mapped trace of the Chino Fault crosses Sapphire Road a couple hundred feet east of the sign. You can look north across the valley and follow the trace of the fault where it disappears into the distant Los Angeles Basin area between Pasadena and San Bernardino with the San Gabriel Mountains in the distance to the north (Figure 1-8). In the foreground you can see the escarpment of the Chino Fault in the vicinity of nearby Alterra Park.

Alterra Park: This small community park is an easy place to get a view of the Chino Fault. Return back down Elvinar Drive and turn right on Soquel Canyon Road. The entrance to Alterra Park is 800 feet downhill on the right. There is a nice parking lot with public restrooms. The Chino Fault (with scarps) passes through the canyon just east of the park playground (Figure 1-9). A small deflected stream drainage reveals the location of the fault on the north side of Soquel Canyon Road.

Butterfield Ranch Road: Continue downhill on Soquel Canyon Road and turn right on Butterfield Ranch Road. Butterfield Ranch Road roughly parallels the Chino Fault as it cuts across the eastern mountain front along the Chino Hills. Note that there is no parking along the road, and it is a bit difficult to pick out fault scarps and associated fault-related features because erosion of the soft sediments quickly modifies landscape features over time.

It is important to note that the historic Butterfield Overland Stagecoach Route basically follow the Elsinore Fault Zone along many parts of its path (Stibbe, 2018). The stage route was active through the Chino area between 1858 to 1861.

Butterfield Ranch Road at Park Crest Drive: An open field area along Butterfield Ranch Road is located on the east side of the road across from the intersection with Park Crest Drive. This grass-covered slopes in this area displays landscape features that hint of the local fault zone including offset streams, side-hill benches, and scarp, although they are heavily eroded (Figure 1-10). Signs say "keep out" and there is no parking on the road, but you can see local folks walking their dogs on the uphill old road grade of Park Crest Drive (closed to traffic). The road crosses the fault about 1000 feet up the old road.

Butterfield Ranch Elementary School: Continue south on Butterfield Ranch Road and turn right on Mystic Canyon Drive. The parking area for Butterfield Ranch Elementary School is on the left about a half-mile up the road. The Chino Fault is mapped crossing through the parking lot (not visible because is was scraped during construction). However. the fault scarp associated with a pressure ridge is behind an just north of the school building (Figure 11). The fault crosses Mystic Drive and trend northward across the steep and eroded hillside north of the school. A lone oil well can be seen on the hillside above the fault zone (Figure 1-12).

Whittier Fault Section

Chino Fault (southern part)

Glen Ivy Section (Elsinore Fault Zone)

Glen Ivy Section (Modified from SCEDC summary)

• TYPE OF FAULT MOTION:  Right-lateral (dextral) strike-slip with some reverse or oblique displacement (resulting in development of the trough); most of the dextral slip occurred on the Glen Ivy North strand. Both horizontal and vertical displacement is observable in the Temescal Valley.
• ORIENTATION: There are multiple fault strands within this section. Average strike is N54°W (for section); Dip: 15° SW. to 90°; variable vertical (oblique slip) components for each of the faults. The Glen Ivy North and South faults are more steeply inclined, and seismicity suggests a southwest dip to about 12 km depth (Hull and Nicholson, 1992).
• LENGTH:  about 29 miles (46 km)
• LOCATION: Riverside County, California.
• NEAREST COMMUNITIES: Corona, El Cerrita, and Elsinore, CA
• MOST RECENT SURFACE RUPTURE: Historic surface rupture occurred on 15 May, 1910; Holocene activity has been reported for the length of the fault zone.
• INTERVAL BETWEEN MAJOR RUPTURES: Estimates from different locations along the faults range between 200 yr to <960 yr.
• PROBABLE MAGNITUDES: 
• SLIP RATE: about 5 mm/yr
• GEOMORPHIC EXPRESSION: Graben (including Temescal Valley),scarps, saddles, swales, depressions, deflected drainages, faceted spurs, displaced Holocene and Pleistocene alluvium and alluvial fan, marsh, and landslide deposits.
• QFFDUS ID: Glen Ivy section (126c); named by Engle, 1933; other names used for fault strands within the area include Eagle, Fresno, Tin Mine, Gypsum, and Main Street faults.

Study Area 2 - Chino and Glen Ivy Sections

Study Area 3 - Glen Ivy section

Places to check out (north to south):

To continue on the tour south from the Skyline Drive stop, follow Foothill Parkway about 4.5 miles south to Interstate 15. Turn right on Bedford Canyon Road (the frontage road on the west side of the interstate). Take Bedford Canyon Road one mile and turn right on Eagle Glen Parkway. Follow Eagle Glen Parkway to where it dead-ends at the Eagle Glen Golf Club.

Eagle Glen Golf Club: The Eagle Glen Golf Club is a good place to get an appreciation of the Elsinore Fault (Glen Ivy section) and take in the scenic view of Bedford Wash Canyon cutting into the Santa Ana Mountains (Figures 3-5 to 3-10). The fault runs across the valley of Bedford Wash just west of the clubhouse. From the restaurant balcony overlooking the golf course in the broad wash valley it is easy to see a linear pressure ridge and sag ponds lined up cutting across the valley (although they were modified somewhat during the construction of the golf course). The clubhouse might be a good place for lunch and take some scenic photographs of the faulted landscape around the golf course (or even hit some golf balls!). Several fault strands of the Glen Ivy Fault Zone cut across the golf course in the wash valley.

Mathews Dam View off of Cajalco Road: Return back down Eagle Glen Parkway to Interstate 15. If you continue straight on Cajalco Road east of the Interstate, it is about 4.5 miles to drive up to Lake Mathews Dam (Figure 3-11). At the top of the mountain turn left on La Sierra Avenue. You can take in the scenic view to the west of the flat mesa top of the area (the old erosion surface on top of the Perris tectonic block; Figure 3-12). From this location is is also easy to see the relative even erosion surface that defines the skyline of the Santa Ana tectonic block on the west side of the Elsinore Fault Zone (rift valley).

Clay Canyon Drive/Wildrose Ranch Community Park: If you choose to skip driving up to Lake Mathews, get on Interstate 5 at the Cajalco Road (Exit 91) and head south one mile to the next exit (Weirick Rd./Dos Laqos Rd., Exit 90). Turn right, and then left on Knabe Street. Knabe Street parallels the interstate south for about a mile before it curves to the west. In 1/4 mile turn right on Clay Canyon Drive. Clay Canyon Drive loops back around to Knabe Street at Wildrose Ranch Community Park (park anywhere it is safe). The Glen Ivy section of the fault runs along the mountain front next to Clay Canyon Drive. A trail in this small park follow a scarp/shutter ridge through the park to Knabe Street. On the opposite side of Knabe Street from the park, the fault crosses the deflected stream drainage of Stone Canyon Creek.

Continue south as Knabe Street turns into Trilogy Parkway. Trilogy Parkway dead-ends on Temescal Canyon Road. Turn right on Temescal Canyon Road and proceed to the next intersection and turn right on Glen Ivy Road. Glen Ivy Road leads to the parking area for Glen Ivy Hot Springs (a historic spa resort) (continued below with Study Area 4).

Area 4 - Glen Ivy section

Temecula Section (Elsinore Fault Zone)

Temecula Section (Modified from SCEDC summary)

• TYPE OF FAULT MOTION: Right-lateral slip on parallel fault strands, displaying oblique slip at a ration of about 1:10.
• ORIENTATION: Strike of faults is roughly N48°W; dip angles are steep to the SW and NE. Seismic data suggests a near-vertical to steep NE dip to about 13 km depth.
• LENGTH:  39 miles (62 km)
• LOCATION: Riverside and San Diego Counties
• NEAREST COMMUNITIES: Lake Elsinore, Wildomar, Temecula, Murietta, and Pala, California
• MOST RECENT SURFACE RUPTURE: unknown.
• INTERVAL BETWEEN MAJOR RUPTURES: 250–600 yr. (or more)
• PROBABLE MAGNITUDES: 
• SLIP RATE: Between 1.0 and 5.0 mm/yr
• GEOMORPHIC EXPRESSION: Northern end of Temecula section is comprised of the Willard and Wildomar faults along south side of Lake Elsinore. Features along the Wildomar Fault include horst, scarps, sag ponds. Fault features along the Willard Fault include linear mountain front, faceted spurs, low scarps in alluvium. Where the Elsinore Fault crosses Agua Tibia Mountain near the southern end of the Temecula section it produces offset streams, beheaded drainages, shutter ridges, and a graben.
• AGE OF FAULTED SURFACE DEPOSITS: Holocene alluvium and fan deposits; late Pleistocene Pauba Formation (Wildomar, Murrieta Creek and Wolf Valley faults); late Pleistocene Pauba Formation (Willard fault) (Kennedy, 1977).
• QFFDUS ID: Temecula section (126d)
  

Study Area 5 - Glen Ivy and Temecula Sections

Study Area 6 - Temecula Section

Places to check out (north to south):

From the Lake Elsinore Vista Point, follow the Ortega Highway 74 back down to Grand Avenue and turn right (south).

Willard Fault near Grand Avenue: As you drive southeast along Grand Avenue you are basically following the Willard Fault on the southwest side of the Elsinore Trough. The Willard Fault is mapped as a series of smaller, parallel and interconnecting fault along the lower mountainside and as strands buried in the alluvial fan sediments along the trough margin. The expression of the fault includes the linear mountain front with faceted spurs, hour-glass canyons, and older (degraded) side-hill benches.

Wildomar Fault Scarp at Serenity Park: Follow Grand Avenue south about 5 miles and turn left on Corydon Road. Follow Corydon Road east about a half mile to Palomar Street. Turn left on Palomar Street and look for a parking spot. A well-developed linear fault scarp of the Wildomar Fault runs along the border of the park (Figure 6-5).The bedrock on the uplifted side of the fault is sedimentary deposits (Late Pliocene to Early Quaternary) whereas Late Quaternary lacustrine (lake, marsh, and alluvial deposit) underly the lower area below the escarpment. During wet periods during the Ice Ages the larger ancient Lake Elsinore extended into this basin area.

Wildomar Fault along Palomar Street: Continue south on Palomar Street for 5 miles to the next stop. Along the drive you can see a lot of features associated with the trace of the Wildomar Fault (it is mapped as part of the Temecula section of the Elsinore Fault Zone; this section of the fault is named for the community of Wildomar in this area). The fault basically parallels Palomar Street on along the slopes its northeast side of the street . The fault trace appears a series of low hills (or knolls) that are pressure ridges, shutter ridges, swales, and a low linear scarps (a small swales occur on the south side of the street as well). The bedrock of the uplifted area is soft sedimentary deposits (Late Pliocene to Early Quaternary) so fault-line features are degraded. Murietta Creek flows through the valley parallel to the fault.

Wildomar Fault at Chaney Hill: Palomar Street make a sweeping "S" bend and becomes Washington Avenue into Murietta. However, just before the "S" bend, turn right on Starbuck Circle and park. It is an easy place to park and get out and look at the linear escarpment for the Wildomar Fault at a historic location called Chaney Hill (Figures 6-6 and 6-7). Chaney Hill is an uplifted block on the east side of the Wildomar Fault that consists older basin fill deposits of the Pauba Formation (Pleistocene). This is a famous fossil locality. Vertebrate fauna from the Pauba Formation are of late Irvingtonian and early Rancholabrean ages (2-3 million years). At Chaney Hill in Murrieta area, the unit contains the 700,000 year old Bishop ash (deposits from a massive eruption in the Mammoth Lakes volcanic area on the eastern side of the Sierra Range). Estimated maximum thickness of the Pauba Formation is 75 meters (Kennedy & Morton, 2003).

View of Elsinore Peak: If you look west from the Wildomar area you can see Elsinore Peak (elevation 3,566 feet), the highest peak in this part of the Santa Ana Mountains (Figure 6-8). The interesting geologic story is that Elsinore Peak is capped by basalt flow deposits that probably flooded a valley that existed along a very different regional coastal landscape before the Elsinore Fault/Elsinore Trough formed. The Basalt of Elsinore Peak is a remnant of black vesicular basalt capping Elsinore Peak. The basalt has been radiometrically dated to be 11.2 to 11.6 million years old (Morton, 2004).

Continue south into Murrieta. At the "S"bend near Chaney Hill Palomar Street becomes Washington Avenue. (Continued is Study Area 7.)

Study Area 7 - Temecula Section

Option A: The Wildomar Fault (urban route)

Wildomar Fault Features along Jefferson Avenue: Jefferson Avenue basically follows the Wildomar Fault south for about 7 miles through downtown Murietta into Temecula (near Old Town). The route passes through both residential and commercial/industrial areas. Although construction has modified the landscape in most areas it is possible to still see low shutter ridges and fault-related swales along a linear trend next to Jefferson Avenue. A particular hilly section along the Wildomar Fault scarp is on the east side of Jefferson Avenue between Guava Street and Elm Street. The fault zone features are visible but degraded, suggesting past (prehistoric) displacements and surface ruptures along the fault zone. The fault offsets very old alluvial deposits of Pleistocene Pauba Formation, a formation consisting of poorly consolidated sandstone, siltstone, and conglomerate (Figure 7-5).

Murrieta Hot Springs Fault: From Nutmeg Street proceed south on Jefferson Avenue for 2.3 miles to Ivy Street. The Murrieta Hot Spring Fault crosses Ivy Street near the Interstate 15 overpass. The Murrieta Hot Springs Fault runs roughly perpendicular to trace of the Wildomar Fault, and it is known to have Quaternary displacement. Murrieta Hot Springs: Early settlers in the Temecula/Murrieta area utilized natural hot water springs that came to the surface in the vicinity of the Murrieta Hot Springs Fault. Murrieta Hot Springs is another set of sulfurous springs located along the Elsinore Fault Zone. These springs had a maximum temperature of 136° that was supplied to a resort hotel that was established nearby in the late 19th century (Waring, 1915). Over the past century warm springs were developed into spa resorts (they are located east of I-15 on Murrieta Hit Springs Road at Margarita Road).

Continue south along Jefferson Avenue into the Old Town Temecula area. Note! You likely encounter heavy car and pedestrian traffic in the Old Town area. You can avoid the heavy tourist traffic by crossing I-5 at Winchester Road, and then take the first right on Ynez Street and proceed to Temecula Duck Pond Park to see the Wildomar Fault in that location (in Study Area 8).

Option B: Willard Fault (rural route)

Willard Fault Zone on Deluz Road: From the Chaney Hills stop follow Washington Avenue south for 3 miles and turn right on Ivy St.
In 1/2 mile turn left on Hayes Avenue.
In 1 mile turn right on De Luz Road. (Figure 7-6).
Follow De Luz Road where ascends a canyon to the top of the Santa Rosa Plateau (located in the southern end of the Santa Ana Mountains).

De Luz Canyon: Along the way, DeLuz Road crosses the Willard Fault about a mile west of Hayes Avenue near where the road begins to ascend steeply up the mountain front. The the land on the north side of De Luz Road is part of the Santa Rosa Plateau Ecological Reserve and Riverside County Parks lands (Figure 7-7). A trailhead parking area is on the left near the mouth of the canyon on De Luz Road. Shortly beyond the parking area the pavement ends and the road becomes packed gravel for the way up the canyon. Along the way you can see linear stream drainages that descend down the side of the canyon north of DeLuz Road. These ravines probably follow follow fault strands that parallel the Willard Fault. Cuts along the road in the lower part of the canyon display highly fracture and contorted bedrock in the vicinity of faulted areas (Figure 7-8). In contrast, near the top of the unpaved road grade west of the fault zone the bedrock is more massive and less fractured (Figure 7-9).

The road comes out of the canyon onto the rolling upland of the Santa Rosa Plateau and Mesa de Burro. Volcanic lava flows (basalt) cap the Mesa de Burro and other parts of the plateau (Figure 7-10). The lava flows have been dated to be about 7-8 million years old. Layers of volcanic rock of similar age occur on the northeast side of Elsinore Trough exposed in the Hogbacks along Los Alamos Road (these were dated to be about 10-11 million years old)(Morton and others, 2006). . How these volcanic areas relate to the possible early stages of the formation of the Elsinore Fault is uncertain. The magma probably found its way to the surface along faults that predate the Elsinore Fault Zone.

The pavement on De Luz Road starts again at the top of the canyon. Continue on for several hundred feet and turn left of Calle Capistrano.
In about 1 mile, turn left on Rancho California Road toward Temecula.
In two miles you will come to the intersection of Avenida del Oro/Sandia Creek Drive (or the right). A small parking area is on the right at the intersection (Figure 7-11).

Temecula Valley Overlook: There is an undeveloped overlook area on Rancho California Road at the intersection with Avenida del Oro/Sandia Creek Drive (or the right). A deeply rutted dirt road (not recommended for driving) is on the north side of the intersection that leads about 1000 feet up to the top of the ridgeline overlooking the Temecula Valley (the location shown on the map on Study Area 8 below). The view is impressive, and it is possible to see the fault trace features for the Willard Fault running along the base of the mountain front including escarpments with faceted spurs, side-hill benches, linear and deflected stream drainages and vegetation contrasts (Figures 7-12 to 7-14).

Along the way down the mountain the road crosses several strands of the Willard Fault near the base of the mountain front. Linear ravines and side-hill benches hint at the location of fault lines. At 5 miles, Rancho California Rd intersects Jefferson Avenue in Old Town Temecula. (See the map for Study Area.8.)

Study Area 8 - Temecula Section

The local landscape in influenced by Quaternary uplift of the mountain front on the west side of the Willard Fault. North of Temecula Canyon is the Santa Rosa Plateau, part of the the southern end of the Santa Ana Mountains. South of Temecula Canyon is Pueska Mountain.

Temecula is spread out into three alluvium-filled valleys:

• to the northeast is Temecula Valley (along Murrieta Creek),
• to the southeast is Wolf Valley (along Pechanga Creek),
• to the northeast is Pauba Valley (along Temecula Creek), and;
• to the south is the smaller Rainbow Valley (a canyon along Rainbow Creek).

Optional Route A - Wildomar Fault Crossing 1-15 (and avoiding Old Town Temecula)

Optional Route B - Head straight to Temecula Duck Pond Park

Optional Route C - Proceed through Old Town Temecula to the Temecula Canyon area

Wolf Valley - Temecula to Pechanga

Julian Section (Elsinore Fault Zone)

Julian Section (Modified from SCEDC summary)

• TYPE OF FAULT MOTION: Right-lateral and reverse (oblique slip)
• ORIENTATION: Strike: N56°W, Dip: near-vertical to 45°, NE
• LENGTH:  49 miles (79 km)
• LOCATION: San Diego County, across the high peaks region of the Peninsular Ranges into the Anza Borrego Desert region (State Park)
• NEAREST COMMUNITIES: Pala, San Felipe, Julian, CA
• MOST RECENT SURFACE RUPTURE: Latest Quaternary (<15 ka); no large earthquakes in this section in historic time
• INTERVAL BETWEEN MAJOR RUPTURES: unknown, possibly 340 years
• PROBABLE MAGNITUDES: Mw 6.0-7.0
• SLIP RATE:  between 1.0 and 5.0 mm/yr
• GEOMORPHIC EXPRESSION: dextral deflected drainages, shutter ridges, hillside benches and scarps in alluvium, offset and beheaded drainages, benches and scarps along both the main Elsinore Fault and the the nearby Earthquake Valley Fault. Displacements are observable in Holocene alluvium and Quaternary alluvial deposits.
• QFFDUS ID: Julian section (126e)

Study Area 9 - Temecula Section and Julian section

Study Area 10 - Julian section

Geologic map: Kennedy, 2000 (left side); Kennedy, 2014 (right side).

Places to check out (north to south):

At the intersection of Highway 76 in Pala, turn left (south). The highway follows the valley of the San Luis Rey River into Pauma Valley.

Elsinore Fault scarps on Adams Drive: About 5 miles south of Pala, Adams Drive is on the left (east) side of the road. A strand of the fault crosses of the fault about 1,000 feet up the road at the intersection of El Sendero Dr. The change in slope in this area basically reveals the location of the fault cutting across the old alluvial surface (somewhat hidden in the local orchards). If you continue up the road to the next intersection at Paseo Lindo, on the left is a dirt road called the Gomez Trail that heads up the mountains. Here you can get above the orchards and get a view of the valley with the faceted spurs along the mountain front. You can continue for about a mile as Adams Drive winds along the mountain front before it descends back in the valley, connecting with Pauma Reservation Road before intersecting back with Highway 76.

From the stoplight at Pauma Reservation Road, turn left (east) onto Highway 76. In 1.2 miles Nate Harrison Grade (road) is on the left.

Nate Harrison Grade: The Nate Harrison Grade is a historic trail, now an unpaved 4WD Road that connects Pauma Vally to the park road in Palomar Mountain State Park. Note that this is a relatively narrow, often single lane, mountain road, without guardrails on steep mountainsides. It is not recommended for passenger cars, and most vehicles drive the route coming down the mountain from Boucher Hill in the state park. The lower part of the road is paved up the alluvial fan to the base of the mountain front (Figures 10-5 and 10-6). The trace of the Elsinore Fault crosses the road somewhere in the vicinity of 2,800 ft overlook (Figure 10-7). The fault is not obvious along the road, but strands of the fault can be seen at notch on Eagle Crage Mountain to the north (Figure 10-7), and along the mountain front along Pauma Valley in the Adams Drive area discussed above (Figure 10-8).

Harrison Canyon is the deep gorge on the south side of the Nate Harrison Grade. Erosion along the fault line is expresses a a notch in the ridgeline on the south side of the canyon (Figure 10-9 and 10-10). The fault trace continues south along the mountain front on Palomar Mountain. Palomar Mountain (see website) is part of a great uplifted block of basement rocks (metamorphic and granitic rocks of Mesozoic age) on the northeast side of the Elsinore Fault Zone. The linear mountain front stretches near 17 miles from near Pauma to Lake Henshaw (to the south).

Witch Creek Fire Burn Area: Witch Creek Fire (or Witch Fire) occurred in October of 2007 after and merged with the Poomacha Fire (Figure 10-11). It was the most widespread and destructive wildfire in the San Diego region in modern history. Much of the mountainous country east of Palomar Mountain burned in the fire, and evidence in the form of burned stumps still can be seen across the region today. Note there have been numerous other small (and destructive) fires in the area since then.

Continue south of Highway 76 to Study Area 11.

Study Area 11 - Julian section

Study Area 12 - Julian section

Lake Henshaw Dam was constructed in 1923 on the San Luis Rey River near the mouth of the linear canyon that follows the Elsinore Fault Zone. Unfortunately, the dam area is inaccessible but you can see it from a pull off area along the north side of Highway 76 (Figure 12-11). The earthen dam is 123 feet (27 m) tall and 600 feet (200 m) long and has the capacity to hold 55,000 acre-feet of water. It was built to supply Vista with a reliable water source, primarily for agricultural irrigation (now about 70% goes for residential use). The Vista Irrigation District owns the reservoir and the surrounding land of Warner Springs Ranch. Lake Henshaw Resort provides access to fishing on Lake Henshaw and provides campsites, lodging, a store and restaurant.

Henshaw Pull Off: About a mile southeast of the Lake Henshaw Resort is a pull off area on the north side of Highway 76 that is a good place to get a look at the shoreline of the lake and the the mountain front of Mesa Grande . The mapped trace of the Elsinore Fault runs across the road in this area but it is not particularly obvious. However, you can see variety of swales and degraded scarps exposed in the grasslands between the lake and the highway (Figures 12-12 and 12-13),and between the highway and the steep break in slope on the forested mountain front of Mesa Grande (Figure 12-14). This pull off is a good place to observe Monkey Hill, a granitic inselberg (horst block) in the middle of Henshaw Valley along the east shore of Lake Henshaw.

Morettis Junction pull off: Highway 76 basically follows the trace of the fault along the south shore of Henshaw Lake and Warner Basin to Morettis Junction. Morettis Junction is the name of the intersection of Highways 76 and 79 at the southeast end of Warner Valley. Less than a quarter mile west of the intersection is a pull off area on the north side of Highway 76. This is a good location to observe the regional landscape features and structures associated with the local fault zones. To the west, the Elsinore Fault Zone follows the straight mountain front along the north side of Mesa Grande and continues into the canyon of the San Luis Rey River (Figure 12-15). The junction is located near the confluence of two faulted linear canyons of Carrizo Creek and Callisto Creek (Figure 12-16). Small swales, scarps and other fault related features can be seen in the grasslands near Morettis Junction (Figures 12-18 and 12-18). South of Morritis Junction, Highway 79 mostly follows the Elsinore Fault Zone along the linear Carrita Creek Valley between Mesa Grande and the Volcan Mountains.

From Morettis Junction continue south on Highway 79 to Study Area 13.

Study Area 13 - Julian section

Geologic map: Santa Ana 1:250,000 (1965); SE corner: Todd (1994).

Places to check out (north to south):

Carrita Creek Valley: From Morritis Junction on CA Highway76 turn right (south) on CA Highway 79. Highway 79 follows the Elsinore Fault Zone through the Carrita Creek Valley along the linear mountain front along the east side of the highway. The highway follows the fault line for about 3 miles where the road crosses a low divide. South of the divide Highway 79 and bears to the right (east, away from the fault line) in the vicinity of the Santa Ysabel Tribal offices and community. However, the fault zone continues to the southeast passing through the private lands of Santa Ysabel Reservation along School House Canyon Road. Unfortunately, there are no places to easily stop along Highway 79 to see the fault.

Santa Ysabel East Preserve: From there Highway 79 descends into the Santa Ysabel Valley and in 4 miles intersects with Highway78 in Santa Ysabel (community). Just before you arrive in Santa Ysabel, a short road on the left (east) leads to the Santa Ysabel Nature Center, located at 22135 Highway 79, Santa Ysabel, CA 92070 (Figure 13-5). The Nature Center celebrated its grand opening in December 2019. It is well worth the visit. Trailheads near the Nature Center are for paths that lead up into the high country of the Santa Ysabel East Preserve. Figure 13-6 shows a view of the Santa Ysabel Creek Canyon that follows the trace of the Elsinore Fault into the high country of the Volcan Mountains. Views of the fault canyon are accessible from along the Coast to Crest Trail and the Santa Ysabel Loop Trail that passes through the preserve lands. Figure 13-7 is a view of the ridgelines on both sides of the Elsinore Fault Zone in the Volcan Mountains as seen looking east from along Highway 78 on the opposite side of the Santa Ysabel Valley.

The Coast to Crest Trail also connects with the Kanaka Loop Trail. At its eastern end the Kanaka Trail that follows along the Elsinore Fault that follows the drainage of Santa Ysabel Creek in the eastern part of the preserve. A parking area for that Kanaka Trailhead is located on Farmers Road, about 3 miles north of downtown Julian (see map Figure 14-1). To get to a Kanaka Trailhead parking area at the east end of the Santa Ysabel East Preserve from the Nature Center, take Highway 79 into Santa Ysabel (community) and turn left (east) onto Highway 78. . At the intersection with CA Highway 78 turn left and drive 7 miles into downtown Julian. At the main intersection in town turn left (north) on Farmers Road. The Kanaka Trailhead parking for the Santa Ysabel East Preserve is 3 miles north out of town and on the left. You will pass the Volcan Mountain Preserve Trailhead on the way (discussed below).

Continue to Study Area 14.

Study Area 14 - Julian section

Geologic map: Todd (1994), see map legend (Figure 14-5). Figure 14-6 is a map of the physiographic provinces of San Diego County. The Elsinore Fault is the dividing line between the Santa Ana tectonic block to the west and the Fault-bounded Blocks and Basins region to the east (encompassing Anza Borrego Desert State Park). The contrast of these two regions can be seen can be seen within a few miles drive east or west of the town of Julian.

Julian, CA: The Julian area experienced a gold rush started in 1870 that lingered to about 1900. The area then prospered as an apple farming district and as a mountain recreation destination. Today, the town of Julian is a major tourist destination and can be extremely crowded on weekends practically any time of year. Julian is located along the crest of the Peninsular Ranges in a divide between the Volcan Mountains to the north and the Cuyamaca Mountains to the south (accessible along the scenic Skyline Highway (CA 79). Individuals interested in camping the the area may want to consider making reservations at the campground at nearby William Heise County Park. Figure 14-7 is a topographic map that highlights many of the landscape features in the Julian area.

Places to check out (north to south):

Santa Ysabel East Open Space Preserve: Continue north along Farmers Road to the parking ares for the Santa Ysabel East Open Space Preserve (continued from Study Area 13 above). Farmers Road crosses the Elsinore Fault Zone about a quarter mile north of the Volcan Mountain Trailhead. The Santa Ysabel East Preserve parking area is about a mile north of the Volcan Mountain trailhead area (Figure 14-8). From the parking area it is an easy hike along the Kanaka Trail that follows Santa Ysabel Creek westward for about 1.5 miles along the Elsinore Fault Zone. Along this stream valley is a prominent forest-covered fault scarp that runs south side of the valley. The forest-covered slope on the south side of fault stands out in contrast with the grassy pasture land on the north side of the stream (Figures 14-9 and 14-10). See trail map/ brochure: www.sdrp.org.

Volcan Mountain Wilderness Preserve Trailhead Area: From the main intersection in downtown Julian follow Farmers Road north about 2 miles and park along the road near the Volcan Mountain Trailhead near the intersection of Wynola Road (Figure 14-11). This is a popular day-use only hiking area. The Elsinore Fault Zone crosses the valley between the parking near the trailhead and where the trail start uphill at the Hubbell Gate. The fault zone is about a quarter-mile wide in this area and trail crosses a low shutter ridge near the trailhead. The hike to the top of Volcan Mountain is moderately strenuous—about 5.4 miles round trip starting at 4,100 feet at the trailhead and 5,353 feet at the summit (Figure 14-12). See trail maps/brochures: www.sdrp.org or sdparks.org.

Inspiration Point (Desert View Park): The scenic drive south from Julian on the Sunrise Highway (CA 79) follows the crests of the Peninsular Ranges through the Cuyamaca Mountains. A day trip or weekend camping trip in this forested region is ideal in the warm season. About 3 miles south of downtown Julian is Desert View Park (Inspiration Point), a small park with an sweeping view of Anza Borrego Desert region from the ridgeline above Banner Canyon (the linear stream valley that follow the Elsinore Fault Zone). This is a good location to take in the regional geographic and geologic setting (Figure 14-13).

Banner Canyon: Return south on Farmers Road and turn left (east) on Wynola Road. Wynola Road descends into Banner Canyon near the intersection of CA 78 (be cautious turning left onto the highway 78). Highway 78 through Banner Canyon is a very curvy road as it descend into the valley. Banner Canyon is a linear valley that follows the trace of the Elsinore Fault Zone (Figures 14-14 to 14-17). Unfortunately there are no stops along this highway on the downhill to stop and get out to look at the fault-related along the fault line until you get to the Banner Recreation Ranch area. There are a couple pull offs on the uphill direction (westbound) but be very cautious stopping at pullouts on this busy mountain highway.

Banner Recreation Ranch Area: The Elsinore Fault crosses CA 78 in the vicinity of Banner Recreation Ranch (a roadside stop on the north side of the with fee camping, cabins, and shuttle services for hikers accessing the Pacific Crest Trail. The fault zone follows straight canyon up the mountainside on the south side of the highway (just south of the Banner Recreation Ranch parking lot in front of the small store, Figures 14-18 and 14-19).

Rodriguez Truck Trail: The Rodriguez Truck Trail intersects CA 78 at the bend in the highway near the Banner Recreation Ranch. This is a rugged 4WD road that ascends the mountainside beginning with about a mile drive (or hike) along Chariot Canyon before turning back south to intersect the the Elsinore Fault Zone. From there the truck trail winds through rugged county where there are an abundance of fault-related landscape features, including shutter ridges, offset streams, beheaded streams, and scarps. The truck trail crosses a divine in the vicinity of the fault and continues southward along Vallecito Wash Canyon into the Anza Borrego Desert Park region (Figure 14-20).

Study Area 15 - Julian section

Study Area 16 - Julian section

Geologic map: Todd, 2004.

Places to check out (north to south):

Campbell Grade Pull off: The small pull-off on the south side of Highway S2 to only large enough for a couple cars to stop safely. However, it is a good location to stop for a quick look and photo of Vallecito Valley to the south and east (Figure 16-5). It is easy to see the trace of the Butterfield Overland Mail stagecoach route used in 1858 to 1861.The mapped Julian section of the Elsinore Fault steps over to the east from the Mason Valley area (to the west of Campbell Grade). Active earthquake faults are not mapped in the vicinity of the Campbell Grade, partly because colluvium and landslide materials cover most of the slopes. However faulting is probably responsible for the bench-like faceted spurs along the linear mountain front on the north side of Vallecitos Wash, north of Highway S2.

Fault scarps in Vallecito Valley: Two strand of the Elsinore Fault Zone that display Holocene displacement are mapped crossing the Vallecito Valley just east of Lance Ranch on Highway S2. Whereas the fault scarps do not appear obvious along the side of the highway, the down appear obvious as vegetation contrasts from the air (Figure 16-6). About a quarter mile beyond the bend in the highway where the fault crosses the road is a pull off to an area overlooking the valley where it is possible (with binoculars) to observe these vegetation contrasts from the distance.

Vallecito County Park: Vallecito County Park is a 71 acre county park is host to the historic Vallecito Stage Station along the Butterfield Overland Stage Route (1858-1861)(Figure 16-7). The county park hosts a developed campground and requires a small day-use fee. (The park website claims the campground is 10 degrees cooler than the Agua Caliente Campground described below.)

Coyote Mountain section (Elsinore Fault Zone)

Coyote Mountains Section (Modified from SCEDC summary)

• TYPE OF FAULT MOTION: Right-lateral (dextral) strike slip with a vertical component (reverse and oblique slip).
• ORIENTATION: Average strike: N58°W,  NE with reversal to SE on southwestern portion of fault and "dips shallowly to steeply (Rockwell, 1990)
• LENGTH:  21 miles (33 km)
• LOCATION: San Diego County and Imperial County within the Lower Californian Basin and Range (Colorado Desert) region
• NEAREST COMMUNITIES: (none significant in size in area), Agua Caliente County Park
• MOST RECENT SURFACE RUPTURE: About last event 200–300 yr BP
• INTERVAL BETWEEN MAJOR RUPTURES: 600–1000 yr
  
• PROBABLE MAGNITUDES:  Mw 6.0-7.2 (? (based on
• SLIP RATE: Between 2.0 and 4.0 mm/yr
• GEOMORPHIC EXPRESSION: Sags, shutter-ridges, pressure-ridges, deflected and offset drainages, side-hill benches, and scarps in alluvium and alluvial fans. (Rockwell, 1990). Age of faulted surficial deposits: Holocene alluvial and channel deposits; landslides and debris flows.
• QFFDUS ID: Coyote Mountain section (126f)
  

Study Area 17 - Julian and Coyote Mtns sections

In this area the Elsinore Fault Zone "steps over" the Terra Blanca Mountains. The Julian section peters out over northern end of the Sawtooth Mountains and probably continues into the Inner Pasture part of Canebrake Valley. The Coyote Mountains section begins in the Squaw Canyon Area and cuts through Agua Caliente County Park.

Study Area 18 - Julian section and Coyote Mountains section

Study Area 19 - Coyote Mountain sections

Geologic map (southern half): Todd, V.R., 2004.

Places to check out (north to south):

Indian Gorge (Torote Canyon hiking area): About 9 miles south of Agua Caliente County Park is a turn off to a parking area at the mouth of Indian Gorge (Torote Canyon), a canyon in the strikingly white granitic rocks of the southern Terra Blanca Mountains. The Elsinore Fault runs along the mountain front at the mouth of the canyon. A fault scarp cutting across alluvial fans and parallel to the mountain front can be seen north of Indian Gorge (Figure 19-6).

Mountain Palm Springs Campground: The turnoff to Mountain Palm Springs Campground is about a mile south of the Indian Gorge access road. The primitive campground located at the mouth of the Mountain Palm Springs Canyon is within the Elsinore Fault Zone along the mountain front (Figures 19-7 and 19-8). The Mountain Palm Springs Loop is a 4 mile hike that goes through several palm groves along seeks in the canyon (Figure 19-9).

Bow Willow Road: Continue south another mile to the turnoff to the Bow Willow Campground (a primitive campground at the mouth of a canyon about a mile west of Highway S2)(Figure 19-10). The Elsinore Fault crosses the highway in the vicinity of the turnoff to the Bow Willow Campground.. A fault scarp and pressure ridge is visible near the highway just southeast of the intersection. This is an interesting scarp area to examine the character of the sand and gravel beds exposed along the stream bed that show that deposition was impacted by the displacement (including uplift) along the fault (Figures 19-11 to 19-13).

Carrizo Canyon Campground: The turnoff to the Carrizo Canyon Campground is about 1,000 south of the Bow Willow turnoff, but is on the east side of Highway S2. The fault line Elsinore Fault crosses the Carrizo Canyon Campground Road and ascends into the northwestern end of the Coyote Mountains just south of the campground.

Sweeney Pass: About two miles south of the Bow Willow and Carrizo Campground access roads Highway S2 ascends a large switchback of a divide. Unfortunate there is really no good place to stop in scenic pass area. The northern end of the Jacumba Mountains are on the south side of the highway.

Sin Nombre Canyon: The turnoff to Sin Nombre Canyon hiking area is about 3/4 mile east of Sweeney Pass. The canyon is a popular destination for geology hiking trips to examine the variety of mix of sandstone cliffs and igneous and metamorphic rocks in the area with views of the Carrizo Badlands (Figure 19-14). The 4WD road to the parking area near the mouth of the canyon is about 1.5 miles, and the last mile of it roughly follows the trace of fault. The fault is responsible for displacement of the stream channel in the lower part of the canyon.

Carrizo Badlands Overlook: About 1.6 miles south of Sweeney Pass are turnoff to the Carrizo Badlands Overlook (Figures 19-15 and 19-16). This easy car-access overlook is on a north edge of an escarpment overlooking the headwaters of Sin Nombre Canyon. The Elsinore roughly follows the rugged southern mountain front of the Coyote Mountains.

Coyote Mountains Overlook: This (unofficially named) overlook area is about a mile south of the Carrizo Badlands Overlook on an unpaved track that leads about a quarter mile west to an escarpment over upper Montero Wash Canyon. The overlook provides exceptional views of the northeast end of the Coyote Mountains (Figures 19-17 to 19-21). The trace of the Elsinore Fault is well exposed along the base of the south-facing mountain front of Coyote Mountains.

Dolomite Mine Road: About a mile east of the Carrizo Badlands Overlook is the Dolomite Mine Road (and Dolomite Mine Trail)(Figure 19-22). This road leads to abandoned mine ruins where high magnesium calcite (dolomite marble) was mined back in the 1930s. The mines are located along the southern mountain front in the vicinity of the Elsinore Fault Zone.

Study Area 20 - Coyote Mountains section

Laguna Salada Fault section

The southeasterly trend of the Elsinore Fault Zone continues south of Ocotillo, Ca near Interstate 8 as the Laguna Salada Fault Zone. Laguna Salada Fault Zone is in a mostly uninhabited area of Imperial County California and extends south near Laguna Salada (an ephemeral, dry lake bed in northern Baja California, Mexico). The fault zone is associated with a major Mw7.2 earthquake that occurred on Easter (4 April, 2010) that caused considerable shaking and building damage in both San Diego and Imperial Counties, as well as in Baja California. Amazingly, no fatalities were reported.

Laguna Salada Fault Zone (Modified from SCEDC summary)

• TYPE OF FAULT MOTION: A mix of right-lateral strike slip, normal, and oblique slip faulting (Muller and Rockwell, 1995, Rhymer, 2010)
• ORIENTATION: N40°W (for section); Dip: 55–70° SW.
• LENGTH:  44 miles (70 km)
• LOCATION: Imperial County into Baja California, within the California portion of the Basin and Range Province/California Desert region.
• NEAREST COMMUNITIES: Ocotillo and Plaster City, CA; Progresso, Baja California
• MOST RECENT SURFACE RUPTURE: Mw 7.2 earthquake on 4 April, 2010 Baja California Earthquake (occurred on Easter)
• INTERVAL BETWEEN MAJOR RUPTURES: unknown; possibly 1.2 ka reported by Rhymer (2010)
• PROBABLE MAGNITUDES:  Mw6.5 - 7.5
• SLIP RATE: roughly between 2-5 mm/yr (?) (2–3 mm/yr dextral and vertical deformation rate reported by Mueller and Rockwell, 1995).
• GEOMORPHIC EXPRESSION: Scarps on alluvium and bedrock, beheaded streams, deflected and offset drainages. Displacement of both Holocene and Quaternary alluvium and fan deposits.
• QFFDUS ID: Laguna Salada section (126g)

Study Area 21 - Laguna Salada Fault section

Geologic map: western part: Todd (2004); eastern part: Rogers (1965).

Places to check out (north to south):

Yuha Desert Region: The Yuha Desert is the lowlands east of the Peninsular Ranges, south of Anza Borrego State Park (along the Interstate 8 corridor to the Colorado River extending south across the U.S./Mexico border). The landscape is dry, barren country with low rocky tablelands and badlands cut by alluvial washes and some dune areas. The bedrock consists of Pliocene-age continental and fossiliferous shallow marine sedimentary formations.

Juan Bautista de Anza National Historic Trail: This remote unpaved loop road has both historical and geological significance (Figures 21-5 to 21-13). The historical significance of the trail is recorded on the bronze plate on De Anza Overlook Historic Marker (Figure 21-7); the text is quoted below:

The geologic significance of the historic trail is that it is located on an escarpment of gently to steeply dipping strata that has been pushed up by movement along a strand of the Laguna Salada Fault Zone. Late Quaternary-age alluvial gravel cap the top of the 150-foot-high escarpment (a questa), resting unconformably on dipping Pliocene strata exposed nearby in the wash basin to the east. The fossiliferous character of the sedimentary beds in the Yuha Basin area was noted by the Font's Diary in December of 1775 with speculation that a sea beach had reached this area in the past. Pedro Font (1734-1781) was a member of the Spanish expedition, and his diary describes the itinerary, natural resources of the country, the Indians encountered, and stories of the journey. Geologic mapping of recent fault surface ruptures in the area after the 2010 Laguna Salada Earthquake are shown on Figure 21-1.

Yuha Well: Another historic marker located in El Centro, CA (east of study area) describes another historic location known as Yuha Well. Yuha Well is located along Yuha Wash about 2 miles east of De Anza Overlook in the middle of the barren landscape shown in Figure 21-10. The well is associated with a natural seep along the trace of fault that crosses Yuha Wash.

Selected Resources

The links to references below were all active as of 6/22/2021.

Geologic Map of California: California Department of Conservation, California Geological Survey and U.S. Geological Survey. (link)

California Geological Survey, 2021, Alquist-Priolo Earthquake Fault Zones (California Department of Conservation website). (link; map link)

Chester, T, (2013), Field Guide To the Santa Rosa Plateau website. (link)

Chester, T., (2021), Geology of Temecula Canyon: San Diego State Univ. College of Science, Field Stations Program website (link).

City of Lake Elsinore, 2008, Downtown Main Street Historic Buildings (map, 1 p.) (link)

City of Temecula, 2021, History of Temecula (website). (link)

County of San Diego Parks and Recreation, 2021, Agua Caliente County Park (website). (link),

County of San Diego Parks and Recreation, 2021,Welcome to Aqua Caliente Regional Park (2 page brochure). (link)

County of San Diego, Parks and Recreation, 2021, Volcan Mountain Wilderness Preserve (website with map brochure). (link)

Daviess, S.M. and Bramlett, M.M, 1953, The Alberhill and other clay deposits of Temescal Canyon, Riverside County, California: U.S. Geological Survey Open-File Report 53-52. 10 p. (link)

Dorsey,, R.J., 2005, Stratigraphy, Tectonics, and Basin Evolution in the Anza Borrego Desert Region: Geology, 15 July 2005 (reprint, 29 p.). (link)

Dorsey, R.J, Axen, G.J., Peryam, T.C., and Kairouz, M.E., 2012, Initiation of the Southern Elsinore Fault at ∼1.2 Ma: Evidence from the Fish Creek–Vallecito Basin, southern California: Tectonics, V. 31, Issue 2, April 2012, 21 p. (link)

Engel, R., 1933, Geology of the Santa Ana Mountains and the Elsinore trough: Pasadena, California Institute of Technology, Ph.D. dissertation.

Engel, R., 1959, Geology of the Lake Elsinore quadrangle: California Division of Mines and Geology Bulletin 146, 154 p., 7 pls., scale 1:62,500.

English, W.A., 1926, Geology and oil resources of the Puente Hills region, southern California: U.S. Geological Survey Bulletin 768, 110 p. (link)

Erdelsky, P.J., 2020, Topographic Maps of San Diego County, California (index map with links to 7.5 USGS quadrangle map sheets). (link)

Gans, L.O. and Sylvester, A.G., 2016, San Diego County Road S2 - Ocotillo to Warner Springs [from Roadside Geology of Southern California]. (link)

Hough, S.E. and Elliot, A, 2004, Revisiting the 23 February 1892 Laguna Salada earthquake: Bulletin of the Seismological Society of America, v.94, no. 4, p 1571-1578.

Hull, A.G., and Nicholson, C., 1992, Seismotectonics of the northern Elsinore fault zone, southern California: Bulletin of the Seismological Society of America, v. 82, p. 800-818. (link)

Jennings, C.W., 1994, Fault activity map of California and adjacent areas, with locations of recent volcanic eruptions: California Division of Mines and Geology Geologic Data Map 6, 92 p., 2 pls., scale 1:750,000. (pamphlet link)

Kennedy, M.P., 2000a, Preliminary Geologic Map of the Pala 7.5’ Quadrangle, San Diego County, CA: A Digital Database (Version 10). California Geological Survey. 1 Sheet, scale 1:24,000. (link) [left side of Map 10 area]

Kennedy, M.P., 2000b, Preliminary Geologic Map of the Pechanga 7.5’ Quadrangle, Riverside County, CA: A Digital Database. California Geological Survey. 1 Sheet, scale 1:24,000. (map link) (Pamphlet link)

Kennedy, M.P., 2014, Preliminary Geologic Map of the Boucher Hill 7.5’ Quadrangle, San Diego County, CA: A Digital Database (Version 1.2). California Geological Survey. 1 Sheet, scale 1:24,000. (link)

Kennedy, M.P., 1977, Recency and character of faulting along the Elsinore fault zone in southern Riverside County: California Division of Mines and Geology Special Report 131, 12 p.

Kennedy, M.P., Morton, D.M., 2003, Preliminary Geologic Map of the Murrieta 7.5' Quadrangle, Riverside County, California: U. S. Geological Survey Open-File Report 03-189, 1 sheet. (link)  

Lamar, D.L., and Swanson, S.C., 1981, Study of seismic activity by selective trenching along the Elsinore fault zone, southern California: Technical report to U.S. Geological Survey, Final Technical Report 81-4 (see also U.S. Geological Survey Open-File Report 81-882), Reston, Virginia, December 1981, 50 p. (link)

Lawson, A.C., chairman, 1908, The California earthquake of April 18, 1906—Report of the State Earthquake Investigation Commission: Washington, D.C., Carnegie Institution of Washington Publication 87, 451 p. (link)

Loera, D.M. (2003) Geology of the Western Santa Rosa Plateau Ecological Reserve: Department of Geological Sciences, California State University, Fullerton, bachelors thesis 58 p. (link)

Magistrale, H., and Rockwell, T., 1996, The central and southern Elsinore fault zone, southern California: Bulletin of the Seismological Society of America, v. 86, p. 1793-1803. (link)

Miller, R.V., Shumway, D.O., and Hill, R.L., 1991, Mineral land classification of the Temescal Valley area, Riverside County, California: California Department of Conservation, Division of Mines and Geology Special Report 165, 101 p. (link)

Morton, D.M., 2004, Preliminary Digital Geologic Mop of the 30' X 60' Santa Ana Quadrangle, version 2.0. U.S. Geological Survey Open-File Report 99-172, 55 p. (link)

Morton, D.M, Miller, F.K, Cossette, P.M., and Bovard, K.R., 2006, Geologic Map of the San Bernardino and Santa Ana 30' x 60' quadrangles, California. U.S. Geological Survey Open-File Report 2006-1217, 4 map sheets, with geologic report, 199 p. (with or without photos). (link)

Mueller, K.J., and Rockwell, T.K., 1995, Late Quaternary activity of the Laguna Salada fault in northern Baja California, Mexico: Geological Society of America Bulletin, v. 107, p. 8-18. (link)

National Park Service, 2021, Juan Bautista de Anza National Historic Trail, AZ, CA: website (link).

Rockwell, T.K., 1989, Behavior of individual fault segments along the Elsinore-Laguna Salada fault zone, southern California and northern Baja California—Implications for the characteristic earthquake model, in Schwartz, D.P., and Sibson, R.H., eds., Proceedings of Conference XLV—Fault segmentation and controls of rupture initiation and termination: U.S. Geological Survey Open-File Report 89-315, p. 288-308. (link)

Rockwell, T., 1990, Holocene activity of the Elsinore fault in the Coyote Mountains, southern California, in Rockwell, T., ed., Western Salton trough soils and neotectonics: Friends of the Pleistocene, Field Trip - 1990, Guidebook, p. 30-42.

Rockwell, T.K., Gath, E.M., and Gonzalez, T., 1992, Sense and rate of slip on the Whittier fault zone, eastern Los Angeles basin, California [abs.]: Association of Engineering Geologists, 35th Annual meeting, Proceedings, p. 679.

Rogers, T.H. (compiler), 1965, Santa Ana Sheet: Geologic Map of California, (map scale 1:250,000), in Geologic Atlas of California (printed 1979).

Rymer, M.J., Treiman, J.A., Kendrick, K.J., Lienkaemper, J.J., Weldon, R.J., Bilham, R., Wei, M., Fielding, E.J., Hernandez, J.L., Olson, B.P.E., Irvine, P.J., Knepprath, N., Sickler, R.R., Tong, .X., and Siem, M.E., 2011, Triggered surface slips in southern California associated with the 2010 El Mayor-Cucapah, Baja California, Mexico, earthquake: U.S. Geological Survey Open-File Report 2010–1333 and California Geological Survey Special Report 221, 62 p. (link)

San Dieguito River Park (website with trail guides/maps to Volcan Mountain Wilderness Preserve and Santa Ysabel Preserve East). (link)

SCEDC (Southern California Earthquake Data Center), 2021. Earthquake Information: Elsinore Fault Zone (website summary). (link)

Sleeter, B.M., Calzia, J.P., and Walter, S.R., 2012, Earthquakes and faults in southern California (1970–2010): U.S. Geological Survey Scientific Investigations Map 3222, scale 1:450,000. (link)

Snibbe, K., 2018, The longest stagecoach line through California [Butterfield Overland Stage Route]: Orange County Register, (13 September 2018). (link)

Tan, S.S. and Kennedy, M.P., 2000, Preliminary Geologic Map of the Temecula 7.5’ Quadrangle, Riverside County, CA: A Digital Database. California Geological Survey. 1 Sheet, scale 1:24,000. (map link)(pamphlet link).

Treiman, J.A., and Lundberg, M., compilers, 1998, Elsinore fault zone, Whittier section, Fault number 126a, in Quaternary Fault and Fold Database of the United States: U.S. Geological Survey website. (link)

Treiman, J.A., compiler, 1998, Elsinore fault zone, Chino section, Fault number 126b, in Quaternary Fault and Fold Database of the United States: U.S. Geological Survey website. (link)

Treiman, J.A., compiler, 1998, Elsinore fault zone, Glen Ivy section, Fault number 126c, in Quaternary Fault and Fold Database of the United States: U.S. Geological Survey website. (link)

Treiman, J.A., compiler, 1998, Elsinore fault zone, Temecula section, Fault number 126d, in Quaternary Fault and Fold Database of the United States: U.S. Geological Survey website. (link)

Treiman, J.A., compiler, 1998, Elsinore fault zone, Julian section, Fault number 126e, in Quaternary Fault and Fold Database of the United States: U.S. Geological Survey website. (link)

Treiman, J.A., compiler, 1998, Elsinore fault zone, Coyote Mountain section, Fault number 126f, in Quaternary Fault and Fold Database of the United States: U.S. Geological Survey website. (link)

Treiman, J.A., compiler, 1998, Elsinore fault zone, Laguna Salada section, Fault number 126g, in Quaternary Fault and Fold Database of the United States: U.S. Geological Survey website. (link)

Todd, V.R., 2004, Preliminary Geologic Map of the El Cajon 30' x 60' Quadrangle, Southern California, Version 1.0: U.S. Geological Survey Open-File Report 2004-1361, (link), map scale 1:100,000 (link), correlation of units (link), pamphlet, 31 p. (link)

Todd, V.R., 1994, Geologic map of the Julian 7.5' quadrangle, San Diego County, California. U.S. Geological Survey Open-File Report 94-16, (1 sheet with pamphlet). (link)

Todd, V.R., 1978, Geologic map of the Monument Peak Quadrangle, San Diego, CA: U.S. Geological Survey Open-File Report 78-697, (1 sheet with pamphlet) (link)

Todd, V.R., 1977, Geologic map of the Agua Caliente Springs Quadrangle, San Diego, CA: U.S. Geological Survey Open-File Report 77-742, (1 sheet with pamphlet) (link)

U.S. Geological Survey, 1901, Elsinore quadrangle, California (30 minute quadrangle): Scale 1:250,000 [Surveyed in 1897-1898, reprinted in 1909]. (link)

U.S. Geological Survey, 2008, Index of preliminary image maps of the 2007 fires in Southern California (index to Open-File Reports 2008–1029 through 2008–1083, one sheet. (link)

U.S. Geological Survey, 2021, The National Map viewer app (link) - this mapping application was used to make many of the maps on this website.

U.S. Geological Survey, 2021, Historical Topographic Maps - Preserving the Past (includes topoView app). (link)

Turner, S.L., 2006, Geology of the Eastern Santa Rosa Plateau Ecological Reserve: Department of Geological Sciences, California State University, Fullerton, bachelors thesis 59 p. (link)

Vedder, J. G. and Wallace, R. E., 1970, Map showing recently active breaks along the San Andreas and related faults between Cholame Valley and Tejon Pass, California: U.S. Geological Survey Miscellaneous Investigation Series Map I-574; scale 1:24,000. (link)

Vista Irrigation District, 2021, Our History (website). (link)

Volcan Mountain Foundation, 2021, Trails, Maps & VMF's Volcan Mountain Nature Center (link)

Wallace, R. E. (editor), 1990, The San Andreas Fault System, California: USGS Professional Paper 1515, 283 p. (link)

Waring, G. A., 1915, Springs of California. U.S. Geological Survey Water-Supply Paper 338, 432 p. (link)

Warner Springs Ranch Resort, 2021, Warner Springs Ranch History (website) (link)

Winkler, C., and Kidwell, S., 1996, Field Conference: Stratigraphy of a Marine Rift Basin: (Abbott, P.L. and Cooper, J.D., eds, Neogene of the Western Salton Trough, California: The Pacific Section American Association of Petroleum Geologists, Volume 73. (link)

Working Group on California Earthquake Probabilities, 1995, Seismic hazards in southern California—Probable earthquakes, 1994 to 2024: Bulletin of the Seismological Society of America, v. 85, no. 2, p. 379-439. (link)