Within the National Park System lie some of this nation's most amazing caves. Grand caverns and solution formations usually come to mind when caves are mentioned. Pinnacles, though, has a much different type of caves in structure and formation. The talus caves of the park were formed when steep, narrow canyons filled with a jumbled mass of boulders from the cliffs above. The canyons are the result of faults and fractures in the central area of volcanic rock. These shear fractures filled with gigantic toppled boulders are clear windows into the geologic wonder of the park.
Pinnacles National park has two main areas of caves; the Bear Gulch Caves are near headquarters in the East District, and the Balconies Caves are near Chaparral Campground in the West District. A few poorly documented areas of small talus caves are scattered around. The rockfall that filled the fractures is thought to have occurred during the last series of ice ages. Despite the age of this formation, the process of rockfall and weathering continues. The boulders range from a few ounces to thousands of tons. Much of the rock matrix is supported by gravel and sand that has become lodged between the boulders, or has formed at the contact points of the stones over the centuries. These smaller particles are particularly susceptible to erosion during the flash floods that occasionally rush through the caves.
There is no known evidence of Native American habitation in any caves, though extensive archeological work is yet to be done, and local Native (Mutsun and Chalone) stories have largely died with their tellers. Non-Indian legends that have survived refer to the use of the caves as a hideout by the notorious central California bandito Tiburcio Vasquez, whose brutal contribution to local history ended with his hanging in San Jose, California, in 1875. Stories of hidden treasure and robber's roosts still cycle through campfire stories and local lore, but the location of Tiburcio's hides seem speculative.
The Civilian Conservation Corps built trails through the caves in the 1930's and these trails have endured many storms and travelers. The stairways and bridges they constructed were needed to navigate the caves without the use of ropes and ladders. Today, the Bear Gulch and Balconies caves are principle attractions for visitors at the park.