QUATERNARY GEOLOGY OF THE MESQUITE LAKE 1:100,000-SCALE QUADRANGLE, CALIFORNIA AND NEVADA

The Quaternary geologic map of the Mesquite Lake 100,000-scale quadrangle depicts process and age characteristics of surficial deposits and generalized bedrock units. The coordinated mapping effort is part of a USGS project to investigate the spatial distribution of deposits linked to changes in climate and to provide framework geology for land use management (http://deserts.wr.usgs.gov). The geologic map and associated database was produced using field methods, analyses of digital elevation models and remote sensing images, and previous mapping. Data collection included age and geomorphic process, lithologic composition, pedogenesis, geomorphic position, pavement maturity, particle size distribution, bulk density, surface roughness, flora, fauna, and digital photographs; all geo-referenced using GPS. The approach provides baseline data for ongoing interdisciplinary research including the characterization of biotic soil crusts and rainfall/runoff characteristics within different deposits.

The area includes N-NW-trending mountains of diverse lithology and locally high relief separated by arid internally and externally drained valleys. Medial to distal alluvial fan deposits are moderately sloping and redistributed by intra-fan drainages while valley floors are composed of fine-grained sediments commonly accompanied by groundwater discharge and playa deposits.

We identified a variety of natural hazards including previously unrecognized faults with Quaternary rupture, debris-flow prone areas, and active eolian features. Faults showing offset in late Pleistocene and older surficial deposits, were traced to older bedrock faults demonstrating continuity in time and kinematics. In the Kingston Range, we identified five regionally extensive, debris-flow sequences; the youngest deposits are intermingled with asphalt and a 1930's vintage automobile. Eolian processes are represented by extensive deposits of sand sheets, dunes, and coppice mounds that locally were linked to anthropogenic disturbance. In the Mesquite Lake Basin, Holocene and active sand deposits record the on-going deflation of older groundwater discharge deposits. Mapping of these features provides a means to infer conditions present through geologic time and a framework in which to forecast future events.