The difference is immediately apparent. You know at once why this park is called Pinnacles. Here you face spires and crags that bear no resemblance to the surrounding smooth, round hills. Abruptly, the pinnacle rock formations dominate the scene.
These rocks are the remains of an ancient volcano. Or rather they are part of the remains, for the rest of this volcano lies 195 miles to the southeast. Sound intriguing? It is all part of the story of the San Andreas Rift Zone, which runs just east of the park, and the geological forces that have shaped the face of the landscape in this part of California for millions of years. It is the story of heat, frost, water, and wind wearing at the rock.
Because of its distinctive geological features, Pinnacles was set aside as a national monument on January 16, 1908. Initial development was undertaken by the Civilian Conservation Corps from 1933 through 1942. Examples of the Corps' work can be found throughout the park.
A Land in Transition
The San Andreas Rift Zone, a series of faults, lies just east of the park. It was created when the Pacific Plate collided with and wrenched off a portion of the North American Plate. Geologists know that rift zones are likely places for volcanoes to occur, for here the earth's crust is broken, allowing the magma from beneath the surface to well up. The Pinnacles are the result of these two factors at work - an ancient volcano and movement along a rift zone.
The story begins more than 23 million years ago when molten rock poured over the surface of the land through fissures that opened as the two plates ground past one another. As the eruptions grew in intensity the cone being built by the volcanic activity grew until a high steep-sided volcano had been formed. Geologists theorize that this volcanic mountain once stood nearly a mile higher than North Chalone Peak, the highest point in the park today. Yet even as this volcano was being formed, its own destruction was at hand, for the Pacific Plate upon which it was located began moving off to the northwest. In time the portion of the volcano whose eroded remnants we now know as the Pinnacles reached its present location, 195 miles beyond its point of origin. All the while, too, erosion, was at work carving and breaking down the once mighty peak to about a third of its original height, sculpting the spires and crags you see today. Nor is the geologic process at an end. Millions of years from now what little will be left of this ancient volcano will have moved off to the northwest.
Geologists have for many years tried to explain why it looks like the eastern coast of South America would neatly fit into the coast of West Africa and why rocks on different continents were the same. Recently the theory of plate tectonics, sometimes called continental drift, has emerged. Basically, it says that the Earth's skin is not one single covering as we might expect but is made up of a series of plates. Imagine for a minute that the Earth is like a basketball: the grooves on the ball are like the junctions of the plates. Both Earth and basketball appear to be composed of a single covering. But unlike the basketball, which is one continuous piece, the lighter plates of the Earth's surface float over the heavier interior. Pressures from the interior sometimes force one plate to bump into, pull away from, or move alongside another. Scientists believe that this is what has caused the Pinnacles to make its northward journey.
The General park map handed out at the visitor center is available on the park's map webpage.For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.
A geology photo album for this park can be found here.For information on other photo collections featuring National Park geology, please see the Image Sources page.
Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.
Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
9" x 10.75", paperback, 550 pages, full color throughout
The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!
Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.
Information about the park's research program is available on the park's research webpage.
For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.
The NPS maintains a searchable data base of research needs that have been identified by parks.
A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.
NPS Geology and Soils PartnersAssociation of American State Geologists
Geological Society of America
Natural Resource Conservation Service - Soils
U.S. Geological Survey
General information about the park's education and intrepretive programs is available on the park's education webpage.For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.