We investigated the mechanism of the distinct deformation styles in fault-bounded crustal blocks in the San Francisco Bay region using a two-dimensional map-view model. The model features a nonlinear, elastoplastic (Coulomb) upper crust, and it includes all the major faults in the region. In addition to predicting accurately the long-term fault-slip rates and stress orientations in the region, the weak-fault model predicts areas of crustal faulting in close agreement with field observations. The most striking feature is the distinct spatial domains of the minimum horizontal principal stress (σ2), which are spatially associated with the distinct deformation styles in the region. Crustal faulting is most likely to occur in areas with the least σ2 value.