Fault Trace at Buck Ridge

This remarkable exposure of the fault zone is visible from route 25 about a kilometer north of the turnoff to the Coalinga road. To all appearances the hillside, part of Buck Ridge, has been sheared off, or perhaps there has been uplift—or perhaps both. One thing about a fault, even a major one like the San Andreas, is that parts of it can be segments of older faults, formed by different forces than those that reactivated them. In the Central Coast Ranges, an older set of structures consisting of folds and shears is oriented at a slight angle to the current plate boundary, and some parts of the San Andreas fault system likely were once thrust faults in the older regime.