Established in 1908 to preserve the incongruent and beautiful rock formations for which Pinnacles is named, the Park originally protected only 2,060 acres. It now encompasses about 26,000 acres in the southern portion of the Gabilan Mountains, one of a series of parallel northwest-trending ridges and valleys that make up the Central Coast Range.

Pinnacles National Park, located near the San Andreas Fault along the boundary of the Pacific Plate and the North American Plate, is an excellent example of tectonic plate movement. The Pinnacles Rocks are believed to be part of the Neenach Volcano that occurred 23 million years ago near present-day Lancaster, California, some 195 miles (314 km) southeast. The giant San Andreas Fault split the volcano and the Pacific Plate crept north, carrying the Pinnacles. The work of water and wind on these erodible volcanic rocks has formed the unusual rock structures seen today.

Fault action and earthquakes also account for the talus caves that are another Pinnacles attraction. Deep, narrow gorges or shear fractures were transformed into caves when huge boulders toppled from above, and wedged in the fractures before reaching the ground. These boulders became the ceilings of the talus caves that now entice not only people, but also several kinds of bats.