GEOLOGIC STRAIN PARTITIONING IN THE EASTERN CALIFORNIA SHEAR ZONE: RIDING CRUSTAL WAVES IN THE MOJAVE DESERT
The crustal waves are perpendicular to the contemporary NNE-SSW regional compression direction and they apparently are contractional in origin. Based on dated alluvial sediments deposited in the troughs, the waves began forming about 4-5 Ma. Their development controlled the origin and downstream expansion of the Mojave River, which drains northward from the central Transverse Ranges. A stratigraphic and structural record of recurrent Pleistocene warping is present north of Victorville where the river crosses the westernmost Bullion Mountains highlands. There, the base of the river deposits is an early Pleistocene (1.2-1.8 Ma) angular unconformity and their top is a deformed, late Pleistocene (60-70 ka) geomorphic surface. Recent arching of the southern Mojave Desert probably also induced incision of the modern Mojave River canyon between Victorville and Barstow. The upper crust of the Mojave Desert may be buckling above a decollement at the base of the seismogenic zone at 7-10 km depth. However, given that extensive strike-slip faulting is occurring in the same region, Quaternary strain apparently is partitioned into discrete components of contraction and dextral shearing.