san andreas fault

noun Geology.

1. an active strike-slip fault in W United States, extending from San Francisco to S California and forming the on-land portion of the western margin of the North American Plate.

A fault in California where the North American and the Pacific tectonic plates meet and slide past each other. (See earthquake and plate tectonics.) A major geologic fault located in California. It runs from San Francisco to near San Diego and has been the source of serious earthquakes. (See also under “Earth Sciences.”)