2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 2
Presentation Time: 8:15 AM


MILLER, David M.1, BEDFORD, David R.1, PHELPS, Geoffrey1, SCHMIDT, Kevin M.1, LIDKE, David J.2, MCMACKIN, Matthew1 and DUDASH, Stephanie L.1, (1)U.S. Geol Survey, 345 Middlefield Road, MS 975, Menlo Park, CA 94025, (2)US Geol Survey, PO Box 25046, Denver, CO 80225-0046, dmiller@usgs.gov

Recent surficial geologic mapping for the Mojave National Preserve has been compiled in a digital database that allows quantitative analysis of the geology for the purpose of evaluating geologic data relevant for landscape dynamics and ecosystem processes, such as deposit textures and the effects of subsequent modification by soil development. The mapping was conducted by the U. S. Geological Survey at 1:100,000 scale by delineating surficial deposits in a minimum of 6 process environments and 6 age classes. Blended deposits and erosional environments such as erosional hillslope areas and pediments complete the geologic unit description. More detailed mapping and surficial process studies are ongoing to augment the 1:100,000 scale mapping. Significant discoveries include: (1) Former wetland deposits that provide information on past hydrologic and climate conditions. (2) Extensive eolian sand sheets and alluvial piedmonts with incorporated eolian sand that are no longer active occupy an area that is 10 times greater than that of the active dunes and sheets. They also exhibit distinct plant and animal communities. (3) Middle (?) Pleistocene eolian sand sheets may indicate that a significant sand source existed long before the Mojave River cut through Afton Canyon to create the modern drainage system. (4) Timing and possible causes of large incision and depositional events in large wash systems. (5) Hydrologic character and vegetation assemblages are strongly correlated with geologic map units. Geographic information system analyses reveal several interesting patterns including that erosional environments account for about 40% of the area with 4% represented by pediments and 36% being hillslope environment. The remaining 60% of the area consists of thick sediments with 9% influenced strongly by eolian sand. Most of the remainder is piedmont environment dominated by deposits that postdate the last glacial maximum, with smaller areas of late Pleistocene and middle to early Pleistocene deposits. Older piedmont deposits have greater spatial affinity for bedrock outcrops. These relationships will be used to define representative landscapes in order to better predict linkages between landscape dynamics.