Surficial Geologic Mapping in the northern Bristol Mountains, CA

USGS geologic mappers walkinbg out an intermediate age (likely middle Pleistocene) alluvial fan surface near Broadwell Mesa, in the northern Bristol Mountains, Kelso Dunes Wilderness Area, Mojave Desert, California. The dark outcrop in the middle ground, just ahead of the mappers, is basalt of Broadwell Mesa (~5.5 Ma), which is truncated by the Broadwell Mesa Fault. This fault is part of the Eastern California Shear Zone, a region of faults in the Mojave Desert, some of which are seismically active, that accomodates between ~20-25% of relative motion between the Pacific and North American plates. Surficial geologic mapping and accompanying data allow us to constrain the location, timing, and slip rates of these faults. This type of work helps resource managers and hasard planners make more informed decisions in preparation for possible earthquakes in the region.