Mesoscale fault slip data were gathered in rocks ranging in age between Cretaceous and Quaternary to evaluate the evolution of regional stress tensor orientations in the San Luis Obispo-Santa Maria area of coastal central California. We applied the numerical inversion method of Carey and Brunier (1974) for fault slip data to obtain a mean direction of the maximum principal stress (σ₁) trending 202°, 5° for the late Pliocene-Quaternary. Similar orientations were determined from data of older units. In many late Pliocene-Quaternary sediments, conjugate sets of reverse faults are present, and based on the Anderson (1951) model of faulting, yield the same northeast-southwest-oriented axis of maximum compression. The predominant joint sets strike 030° and 110°, almost parallel and othogonal to large-scale fold axes of the area.

The northeast σ₁ agrees with the present regional stress tensor determined from focal mechanisms, and indicates that since the late Pliocene the deformation of this area was by northeast-oriented crustal shortening. The slip indicators related to this tensor appear to overprint and often mask most of the indicators related to earlier stress regimes.