The San Andreas Fault is about 800 miles long (1,287 kilometers), stretching from the Mendocino coast south to the San Bernardino Mountains and the Salton Sea. Geologists think the total amount of displacement along the fault is at least 350 miles (563 km) since it formed. For example, the volcanic rocks in Pinnacles National Park south of Monterey match volcanic rocks in Los Angeles County (called the Neenach volcanics). Researchers have measured identical rocks offset by 150 miles (241 kilometers) across either side of the fault. And stream channels with sharp jogs - the channels are offset across the fault line - can be visited in the central California's Carrizo Plain National Monument. "The dominant motion along the fault is primarily horizontal, but some areas also have vertical motion," noted Shimon Wdowinski, a geophysicist at the University of Miami's Rosentiel School of Marine & Atmospheric Sciences who has studied the San Andreas Fault.
For example, sharp cliffs called scarps form when the two sides of the fault slide past each other during earthquakes. On the ground, one can find the San Andreas Fault by looking for landforms it created. Sometimes the boundary is a zone of several smaller faults, one or more of which may break during an earthquake. But viewed up close, there are actually many fractures and faults that mark the zone where the two plates slide past one each other. This narrow break between the two plates is called a fault.
Viewed from space, the San Andreas Fault looks like a long, narrow valley that marks where the North America plate meets the Pacific plate.
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