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Pinnacles National Park


  • Type: Natural Environ

An Ancient Volcanic Field

Rising out of the chaparral-covered Gabilan Mountains, east of central California's Salinas Valley, are the spectacular remains of an ancient volcanic field. Massive monoliths, spires, sheer-walled canyons and talus passages define millions of years of erosion, faulting and tectonic plate movement. - NPS


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Chalone Creek Archeological Sites
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Geography »

Geology

The pinnacles themselves are the remnants of a Miocene volcano that is in an advanced stage of decomposition. Approximately 23 million years ago, rhyolitic magma and other flows were forced to the surface through fissures in a basement of quartz diorite and granite. Later activity developed central vents, and explosions from these vents built up a vast thickness of pyroclastics above the earlier lavas. The action of erosion, the work of water and wind on these pyroclastics, has given rise to the unusual and scenic effects for which Pinnacles is famous.

Located near 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 have originated in the Neenach Volcano, near present-day Lancaster, California. The unique breccias of Pinnacles are only found elsewhere in the Neenach Formation, some 195 miles (314 km) southeast. The displacement of the Pinnacles from its point of origin is a testament to the longevity and importance of the San Andreas Fault, which once split the original volcano. The right lateral movement of this giant transform fault has carried the Pinnacles north at a rate of approximately 0.59 inches (1.5 cm) per year. - NPS

Physiography
Physiographic Feature Tectonic Fault

Data »

Particulars for Pinnacles National Park:
Geographic feature Dormant Volcano
Tectonic plate Farallon plate
Locale Type Natural Environ
Tectonic plate North American Plate
Tectonic plate Pacific Plate
Tectonic Plate Tectonic Plate Movement
Volcanic feature Volcanic field




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