DIGITAL GEOLOGIC MAPPING OF LAKE MEAD NATIONAL RECREATION AREA AND VICINITY: INTEGRATING SOILS, DIGITAL TOPOGRAPHY, GEOLOGY AND MASTER REMOTE-SENSING DATA

Geologic mapping efforts by the USGS in cooperation with the National Park Service and Nevada Bureau of Mines are underway to provide a geologic digital database for Lake Mead National Recreation Area (LAME) and the adjacent areas of SE Nevada, NW Arizona, and SE California. The LAME database will provide baseline information for issues of concern to the NPS such as environmental impact and hazards, ground water supply and quality; urban hazards from floods, debris flows, and earthquakes; and changes to ecosystem, hydrology, and sediments related to dams, Colorado River development, and rapid urbanization. To this end, the geologic information is only part of a larger ArcInfo GIS database of remote-sensing data, NRCS soils database, DEM data, and bathymetric and lake-bottom sediment data.

Geologic mapping for this effort relies extensively on georeferenced airborne MASTER remote-sensing data in combination with digital topographic data in the form of high-resolution DEMs. The LAME and surrounding area has the largest existing NASA set of airborne MASTER lines. The broad spectral range of the MASTER instrument (collecting data in the visible, short-wave infrared, and thermal regions) allows for the extraction of chemical and physical information useful in mapping both bedrock and surficial geology. The thermal regions of the sensor collect data that can distinguish rock-forming silicate mineralogy of bedrock units and silica composition in synoptic views of large arid landscapes. The visible and shortwave regions provide data for establishing relative chronologies of surficial units based on soil development, identifying eolian inputs, and determining source regions for surficial units. This data is interpreted and analyzed through a combination of field-collected surface and rock characteristics, field spectral data, and laboratory spectral data to aid in isolating and characterizing biologic, soil and geologic relationships. The integration of digital topographic data with remote sensing can aide in identifying tectonic activity andlandforms, understanding the inset relationships of surficial units, and providing regional scale landscape development information.