Pinnacles National Monument
Rising out of the chaparral-covered Gabilan Mountains, east of central California's Salinas Valley, are the spectacular remains of an ancient volcano. Massive monoliths, spires, sheer-walled canyons and talus passages define millions of years of erosion, faulting and tectonic plate movement.
Rhyolitic breccia is the rock that the High Peaks and other rock formations at Pinnacles are made of. Rhyolite breccia is composed of lava sand, ash, and angular chunks of rock that were explosively ejected from the Pinnacles Volcano.
Pinnacles National Monument began as a volcano that first erupted about 195 miles south of its present location. It has traveled northward along the San Andreas Fault, and currently moves at a rate of about 2 - 3 centimeters per year.