Pinnacles National Park is one of the best and most accessible places to experience talus caves, which are different from what we think of as caves in the traditional sense. They are not formed of limestone like most caves, but result from boulders falling and choking narrow canyons, creating ceilings, passages, and rooms through the rubble. Pinnacles National Park has two main areas of talus caves; Bear Gulch Cave is near headquarters on the East Side, and Balconies Cave is near the Chaparral Area on the West Side.
Volcanic activity created the Pinnacles over 23 million years ago, with subsequent shaping over the millennia by tectonic forces, weather, and erosion. Canyons and gullies formed around the edges of the hardest of the volcanic rocks that make up the cliffs and peaks of the Pinnacles. As the centuries passed, cliffs bordering these canyons became unstable, shedding rocks and rubble into the canyons below. This rockfall is thought to have occurred during the last series of ice ages. The streams in the canyon bottoms then carried away much of the finer material, leaving behind the largest boulders and the rubble pinned between them. Over the years, the streams have smoothed the boulders and scoured the bedrock around them, creating pools and waterfalls. Although occasional flash floods may move some of the rocks, it would take a major tectonic event to dislodge the massive boulders that form these caves.
The talus caves at Pinnacles not only offer visitors an opportunity to surround themselves with the awe-inspiring results of the geologic forces of volcanism, plate tectonics, and erosion, they also provide valuable habitat to wildlife such as spiders, wood rats, and Townsend’s big-eared bats. We ask visitors to the caves to be respectful to wildlife and to other visitors by keeping their voices low and their flashlights out of others’ eyes.