KINEMATICS AND EVOLUTION OF THE SAN JACINTO FAULT ZONE IN THE SALTON TROUGH: PROGRESS REPORT FROM THE SAN FELIPE HILLS AREA
The SE SFH preserve the most intensely folded sedimentary rocks in the area. We interpret this folding as the boundary between the domain of dextral slip and wrench folding to the NW and a broad domain of transrotation to the SE. The transrotational domain transfers slip from the Coyote Creek (CCF) and Superstition strands to the Imperial and Brawley zones in the SE (e.g., Hudnut et al., 1989) but our work shows that it also interacts the Clark strand. The NW boundary of the transrotational zone is well exposed in the SE SFH. A NE to NNE alignment of faulted en echelon domes near the NW boundary formed atop the NE-striking sinistral Extra fault zone. SE of the domain boundary around San Felipe Creek, Landsat+ Spot imagery reveal a complex network of short NE-striking faults in Quaternary sediment. The meshlike, weakly organized geometry of the transrotating sinistral faults is characteristic of fault zones in their infancy. Gravity data show that the CCF SE of Borrego Mtn. is also in its infancy because it cuts across a preexisting SW-deepening basin and is barely detectable in the gravity field. A major dextral normal fault on the NE margin of the Fish Creek and Vallecito Mountains produced this basin between 3 and 0.5 Ma and may once have been the main strand of the SJFZ. Altogether, these data suggest that transrotation SE of the SFH initiated less than ~0.5 Ma old.