The San Cayetano Fault runs along the northern edge of the Santa Clara River valley in Ventura County, southern California, near the towns of Fillmore and Piru. It is a north-dipping reverse (thrust) fault that pushes mountain rocks southward over the valley within the intensely compressed Transverse Ranges.
This region is squeezed by the big bend of the San Andreas Fault, forcing crust to shorten and pile up along thrust faults like San Cayetano. Rapid uplift here is building the mountains and deforming young sediments across the valley.
No great earthquake has been directly recorded on the San Cayetano Fault historically, but it is considered capable of a magnitude ~7 or larger event and may rupture together with the offshore Ventura fault system. Such a combined rupture could pose a tsunami and shaking threat to coastal southern California.