The San Andreas Fault is part of the Pacific Rim of Fire. The Pacific Plate is under most of the Pacific Ocean. Here in California the Pacific Plate comes inland to form a transverse fault (the San Andreas Fault) with the North American Plate. The fault is called transverse, because the plates move past each other on a level plain.
North of San Francisco the Fault runs out into the Pacific Ocean. The oceanic plate dips under the land, heating occurs, and magma is formed. This action has formed the cascade volcanoes such as Lassen Peak, Mt. Shasta, Mt. St. Helens and other Cascade Mountains.
Four choices to reach the San Andreas Fault in San Luis Obispo County and Adjourning Counties: