GEOMORPHIC AND PEDOLOGIC MAPPING OF IVANPAH VALLEY, NEVADA FOR FLOOD HAZARD ANALYSIS

Combining geomorphic and pedologic unit descriptions and mapping concepts into a single Quaternary geological map provides the user with a 3-D understanding of landform evolution and soil genesis in a landscape that can be used for making a variety of environmental and urban land use decisions. A study of Ivanpah Valley, south of Las Vegas, Nevada (the site of future Las Vegas urban development on desert piedmonts), combines geomorphic and pedologic mapping concepts. The Ivanpah Valley map will provide information that can be used in identifying regions prone to flood hazards prior to local and federal land use. In this study, surface inactivity and soil development are used to determine relative ages for landforms and flood hazard assessment. This work provides a multi-discipline, scientifically based, cost effective product that is beneficial to future land use decisions in this region.

Ivanpah valley is a closed half-graben basin with western mountain ranges composed of Paleozoic limestone spotted with few isolated Mesozoic igneous intrusions, and eastern ranges composed of Tertiary volcanics and Precambrian igneous intrusions. The local geology is reflected in the piedmont alluvium and soil development resulting in two soil types: carbonate rich and clay rich soils. Variations in soil types result from mixing of lithologies and eolian contributions from area playas. Alluvium composition and soil profile development affects landform morphology, vegetative communities, and infiltration and runoff rates. Five geomorphic landforms have been identified ranging from early Pleistocene to recent. These include: ballenas, fan remnants, inset fans, mountain valley fans, and playas. Surface morphologies include: ballena, planar, bar and swale, and bar and channel. Landforms are covered by a creosote/bursage plant community. Infiltration and runoff rates change with surface and soil characteristics. Soil development is an indicator of its age, which directly reflects surface stability and landform age. A comparison of soil development provides a link between surface stability and flood hazards in Ivanpah Valley.