Geology of the New York City Region

15. Pyramid Mountain Natural Historic Area

Pyramid Mountain Natural Historic Area encompasses more than a thousand acres along the southeastern front of the Ramapo Mountains. The bedrock and glacial features in this preserve are spectacular! The preserve straddles NJ Route 511 north of Boonton. A visitor center and parking area is located approximately .5 miles north of the intersection with Taylortown Road on the west side of the road. The preserve has many miles of rugged hiking trails leading through forested mountainsides, along tumbling streams, and to high scenic overlooks. Sections of the trail require relatively long and steep climbs to hilltop overlooks. There are excellent circuit hikes several miles in length on both sides of Route 511. A well illustrated trail map is available at the visitor center.

Pyramid Mountain is on the west side of Route 511. The trailhead at the visitor center leads to a system of routes. These paths lead around, and to the top of the mountain, leading to several barren gneiss outcrops on the hilltops that provide spectacular vistas, and past several room to house-sized glacial erratics. The blue trail is a steep climb to the top of Pyramid Mountain. The view across the valley to the east overlooks Turkey Mountain and the expanse of the Newark Basin along the eastern horizon. Those with more time (and energy) should plan a circuit hike along the white trail. This trail follows the cleared path beneath powerlines for about half a mile before returning to the forests. Along the way are numerous exposures of the bedrock. The rock consists of massive to layered granite gneiss which varies considerably in composition. The majority of exposures are composed of bright-colored rock rich in quartz and potassium feldspar granite, and dark, banded gneiss rich in pyroxene, biotite, and amphibole. Layers of marble found in the area support the interpretation that these rocks were originally of sedimentary origin. The pyroxene-rich gneiss probably represents a small intrusion into this ancient sedimentary sequence. These rocks were all highly metamorphosed in the Grenville Orogeny during Middle Proterozoic time.

About a mile from the visitor center on the white trail is Bear Rock, a house-sized glacial erratic alongside Bearhouse Brook. The impressive size of this block of gneiss reveals the awesome power of moving ice. Other unusual giant erratics in this section of the preserve include Whale Rock (shaped like the head of a great whale) and Tripod Rock (a massive boulder elevated from the ground by three smaller boulders)(Figure 38). Tripod Rock is believed by some to be an ancient astrological site. It appears that some of the rocks around this perched boulder may have been moved into their current positions by humans. Whether these rocks are aligned in some manner with horizon positions of solstices and equinoxes is unknown, but based on the festive crowd gathered around the rocks on such days you might think so. Pedestal rocks such as these are not a completely unique occurrence. Their unusual character, however, may have of interest and they may have served as gathering sites in prehistoric times just as they are today.

Pyramid Rock
Figure 38. Tripod Rock on Pyramid Mountain. The pedestal glacial erratic is believed by some to have archeological significance.

The peak of Turkey Mountain is approximately a mile east of the visitor center. Views from the top of the mountain overlook Pyramid Mountain and Taylortown Reservoir to the west, and Lake Valhalla and the expanse of the Newark Basin to the south and east. A picnic at a mountaintop overlook is an excellent place to view and contemplate the awesome character and history of the Ramapo Fault, located at the foot of the mountain front to the east. (It has been reported to display evidence of recent or near recent movement). One of the exposures of Proterozoic marble has been quarried on the southeast side of the mountain. A green variety of nepheline syenite was found in this area and mined as a substitute for jade in the last century. The age of this nepheline syenite is unknown, but may correspond in age with intrusions of similar rock that intruded in to the Great Valley region to the west between Late Silurian to Late Devonian time.

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Last modified: 3/11/2019