in california is the boundary between the north american and pacific plates
North American Plate On its western edge, the Farallon Plate has been subducting under the North American Plate since the Jurassic Period. The Farallon Plate has almost completely subducted beneath the western portion of the North American Plate leaving that part of the North American Plate in contact with the Pacific Plate as the San Andreas Fault. The Juan de Fuca, Explorer, Gorda, Rivera, Cocos and Nazca plates are remnants of the Farallon Plate.