Point Reyes National Seashore Geology

The Point Reyes Peninsula has long baffled geologists. Why should the rocks of this

craggy coast match Tehachapi Mountains rocks more than 310 miles to the south? The

answer lies in plate tectonics and the continual motion of the Earth's crust. The peninsula rides

high on the eastern edge of the Pacific plate that creeps northwestward about two inches a year. The slower-moving North American plate travels west-ward. In Olema Valley, near Bear Valley Visitor Center, the North American and Pacific plates grind together along the San Andreas Fault Zone. This fault zone contains many large and small faults running parallel and at odd angles to one another. Because each plate cannot move freely, tremendous pressure builds up.

From time to time the pressure becomes too great and the underlying rock breaks loose so that the surface actually moves. This is what happened in the San Francisco Earthquake of 1906 when the peninsula leaped 20 feet northwestward.