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

Part of a USGS project to map Quaternary deposits in the arid southwest, the Ivanpah quadrangle depicts surficial deposits and generalized bedrock units. The quadrangle covers much of the Mojave National Preserve, where the northeast-trending New York and Providence Mountains combine to form prominent high relief compared to adjacent low valleys. Broad pediments and groups of pediment domes also exist. Quaternary basaltic cinder cones and lava flows mantle pediments in much of the Cima volcanic field.

Geologic mapping, conducted using field methods and interpretation of remote-sensing images, delineated geologic deposits by process of deposition. Geomorphic position, surface roughness, pavement maturity, pedogenesis, and inset relations were used to differentiate deposit ages. Eight Quaternary faults exist. Some faults cut middle to early Pleistocene deposits, such as in the Mid Hills. Others cut poorly dated early Quaternary or Pliocene deposits, such as near the town of Cima, in the lava fields, and near Old Dad Mountain, and therefore are of probable Quaternary age. Much younger, but probably not Holocene, faults exist in the Bristol Mountains, where faults cut alluvial fan deposits as young as latest Pleistocene. Pliocene tectonism is indicated by asymmetric mountain ranges and valleys that include tilted Miocene deposits, all cut by Pliocene faults. Apparently, Pliocene tectonic landscapes have not been substantially modified by erosional and depositional processes over 3 to 5 million years. Valley-axis floodplains and playas are sources for eolian sand and dust, as shown be extensive eolian deposits downwind of Soda Lake and Kelso and Ivanpah valleys. Sand-enriched alluvial deposits display a marked change in vegetation and animal habitat, commensurate with expected effects on soil moisture properties of the deposits. Groundwater-discharge deposits, created by past springs and wetlands, are present in Kelso and Shadow valleys, providing markers of past groundwater levels associated with wetter climates during the Pleistocene and early Holocene. Surficial geologic map information correlates with vegetation data, probably because the map units contain information on soil moisture. The geologic map data are used as the primary input for recovery models for desert disturbance.