Pinnacles National Park guide · 1 min read
The Neenach Volcano and the San Andreas Fault
The rock pinnacles that give the park its name are the remains of the Neenach Volcano, which was active about 23 million years ago in the area that is now Lancaster, California.
Scientists link the pinnacles to this volcano because the park's unusual breccias turn up only in Neenach formations elsewhere.
The chain of events begins with plate tectonics. Long ago, the central section of the Farallon plate dove beneath the southwestern margin of the North American plate, building up California's Coast Range and setting off volcanoes. Afterward, the Pacific plate ran into the North American plate and broke off a piece of it, forming the San Andreas Fault Zone. Magma forced its way upward through openings that formed where the plates scraped past one another.
As the Pacific plate pushed north, it split the volcanic field. A large section of the volcanic rock was carried about 195 miles away, while the Neenach Formation stayed behind. The San Andreas Fault continues to run beside the park today.
Uneven wear from erosion and weathering carved the exposed rock into the spires and pinnacles visitors see now. The formations are andesite and rhyolite, and the original volcano has been reduced to about a third of its former height. The talus caves began as boulders tumbled into steep ravines and jammed into the gaps between walls, leaving hollow spaces beneath. Bats now make their homes in these caves.
Hikers can choose from more than 30 miles of trails that wind through the rock formations. Climbers tackle the spires themselves, and visitors can walk into the talus caves. Keep an eye on the sky too, since California condors are sometimes seen soaring overhead.
