LATE QUATERNARY FAULTING AND DISTRIBUTED DEFORMATION IN THE CENTRAL MOJAVE DESERT, CALIFORNIA

Recent geologic mapping in the area from Barstow east to Baker, California, illustrates the complexity of faulting and deformation in this tectonically active part of the Mojave Desert. Based on scarps cutting alluvial fans of several ages, we have identified several previously unrecognized active faults, and conversely have determined that several previously designated active faults ceased activity between ~30 and ~200 ka. Where the dextral Calico and sinistral Manix faults intersect, they are mutually cross-cutting and synchronous. The Manix fault is segmented in ~10 km long intervals separated by bends or left steps, with shortened and uplifted hills present at most steps. Associated with some, and perhaps all, steps are NNW-striking faults that can be traced for tens of km northward, apparently segmenting the tectonic block north of the Manix fault. Also present along the north side of the Manix fault are asymmetric flower(?) structures that display folded late Quaternary, Pliocene, and Miocene sediment, with older strata exhibiting progressively tighter fold styles. Complex zones of closely-spaced north-striking normal faults lie adjacent to the Manix fault at Harvard Hill and Buwalda Ridge, suggesting a component of easterly extension within tectonic blocks adjacent to the fault. Off-fault strain is expressed as broad anticlines and synclines. These collective observations require new models for the active east-striking sinistral faults, since the geometry of these faults where interleaved with dextral faults prohibits vertical axis rotation of blocks. One explanation for these observations is that the area east of Barstow to Soda Lake lies in a sinistral shear zone that strikes east and accommodates movement between relatively undeformed provinces to the north and south. This zone interacts with NNW-striking dextral faults at its west end, where several abandoned and newly formed faults suggest that faults have reorganized during the late Quaternary.