Stream offsets at Wallace Creek, Carrizo Plain, California View northeast across the San Andreas fault showing several offset stream channels. Main channel is offset about 130 m and was incised approximately 3,700 years ago. Channel farther to left on near side of fault has been displaced approximately 350 m, is beheaded, and was incised approximately 10,000 years ago. Small gulches at right display about 9 m offset from the 1857 earthquake. No fault creep is observed here and this section of the San Andreas fault is considered locked.
View direction is east-southeast.
The pressure ridge is part of a complex of similar kilometer-scale ridges elongate parallel to the SAF in the southern Carrizo Plain. Drainages initiate on the rising portion of the pressure ridge, develop, and degrade the topography as it moves past the uplift zone. Detailed mapping indicates that the structure is homoclinal, dipping away from the San Andreas fault. In the zone of maximum uplift, the SAF, and a parallel, southwest-dipping fault in the southwestern third of the pressure ridge, accommodate normal slip, and the central block is uplifted as a horst. After moving through the zone of maximum uplift, material again tilts away from it.