Located near the San Andreas Fault along the boundary of the Pacific Plate and the North American Plate, Pinnacles [National Park] is an excellent example of tectonic plate movement.
The Pinnacles Rocks are believed to be part of the Pinnacles-Neenach Volcanic Field 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. Today, these rocks give many species of plants and animals a place to call home.
Geologic forces have created the landscape of Pinnacles, but a climate of hot dry summers and winter rains has also shaped the terrain. The vegetation of the park transforms each year as the rain stops and temperatures climb; hillsides go from vibrant green to golden brown within days.Source: National Parks Service