Slip Rate and Structure of the Nascent Lenwood Fault Zone, Eastern California

Mapping of a 15 by 3 km Airborne Laser Swath Mapping (ALSM) survey centered on the northern Lenwood fault in the Eastern California shear zone (ECSZ) reveals offset of Late Quaternary strata and illustrates the depositional history of the Miocene Pickhandle and Barstow Formations. Two Late Pleistocene alluvial fan generations, unit K and unit F, were correlated based on surficial weathering and desert pavement characteristics. Cosmogenic 10Be dating of these units yields ages of 38 +/- 4 ka and 240 +/- 40 ka, respectively (1sigma uncertainty). A set of K alluvial fans are offset 30 +/- 5 meters along the fault, yielding a slip rate of 0.8 +/- 0.2 mm/yr (2sigma uncertainty). Total dextral offset of the Lenwood fault is determined to be 1.0 +/- 0.2 km based on displacement of the Lenwood anticline. At its present rate of slip, the Lenwood fault may have initiated as recently as ∼1 Ma. The results of this study combined with other fault slip rates in the central Mojave Desert reveal a pattern of heterogeneous, slow strain accumulation across the ECSZ.