PRELIMINARY SURFICIAL GEOLOGIC MAP OF THE WESTERN HALF OF THE CUDDEBACK LAKE 100 K QUADRANGLE, CALIFORNIA

A USGS surficial mapping project focused on the arid Southwest USA (http://deserts.wr.usgs.gov/) conducted mapping and process studies to investigate landscape development and tectonic evolution. This project includes the Cuddeback Lake 1:100,000-scale Quadrangle located in the western Mojave Desert north-northeast of Los Angeles, between the southern Sierra Nevada and San Bernardino Mountains, in Kern and San Bernardino Counties, California. Geomorphic features include high-relief mountains, volcanic domes, low pediments, broad alluvial valleys, and dry lakes. The mapping area includes pre-Tertiary plutonic, metavolcanic, metasedimentary, and metamorphic rocks; Tertiary sedimentary and volcanic rocks; and Quaternary sediments and basalts. Included in the area are the El Paso, Cantil Valley, and Muroc faults as well as the central segment of the Garlock fault zone and portions of the Lockhart and Harper fault zones. The tectonically active western Mojave Desert and the variety of surficial materials have resulted in distinct geomorphic features.

Surficial map units are identified by field observation and remote sensing interpretation; they are classified by depositional process and age using inset relations, pedogenesis, desert pavement development, and type of parent material. The timing of deposition, geomorphic expression, and nature of alluvial, groundwater discharge, wash, and eolian deposits are being analyzed to determine landscape development patterns. These patterns include timing and rates of erosion and deposition, distance from mountain front, and style of drainage development. The analysis will yield previously unknown spatial and temporal relationships between mapped units that aid in understanding the influence of late Quaternary tectonics, and source lithology.

Preliminary results show that the tectonically active area near the Garlock fault zone influenced development of drainage networks; base level was controlled by fault offset. There is evidence of a late Tertiary drainage network preserved in remnants of alluvial fans and paleo-drainage deposits near the Garlock and El Paso fault zones. Previously unmapped Holocene and late Pleistocene fault strands were identified near the Rand Mountains. Mapped faults in the Fremont Valley are tentatively identified as surficial expressions of the buried Cantil Valley fault.