INTEGRATING GEOPHYSICS, GEOLOGY, AND HYDROLOGY TO DETERMINE BEDROCK GEOMETRY CONTROLS ON THE ORIGIN OF ISOLATED MEADOW COMPLEXES WITHIN THE CENTRAL GREAT BASIN, NEVADA

Riparian meadow complexes found in mountain ranges of the Central Great Basin physiographic region (western United States) are of interest to researchers as they contain significant biodiversity relative to the surrounding basin areas. These meadow complexes are currently degrading due to stream channel incision that alters the associated ecosystems. The Great Basin Ecosystem Management (GBEM) project is a multidisciplinary program that is focused on the understanding and restoration of these riparian complexes. One feature of interest is the geometry of bedrock beneath the meadows, especially in areas where alluvial fans at the downstream end of the meadows are present. It is hypothesized that side-valley alluvial fans interact with fault-related bedrock steps to constrict ground water flow and raise the water table, creating wet meadows. Testing this hypothesis (or alternatives that result from examining the data) is critical in the development of a logical, long-term, and robust management plan for protecting and restoring existing meadow complexes. Seismic and ground penetrating radar (GPR) geophysical surveys have been conducted in six riparian meadow complexes in the Central Great Basin from 2003-2005. Over 8 km of seismic profile and more than 70 GPR profiles (in 2D and pseudo-3D) have been collected. These data yield information directly on depth to bedrock. In addition, the seismic data yields deeper structural information on the nature of bedrock topology variations while the GPR data yields near-surface information on the bedrock-controlled stratigraphic variability. The fusion of the two geophysical techniques, therefore, will provide more information than would be available otherwise (using only a single imaging technique) to understand the bedrock and associated sedimentology controls on the meadow formation. These data will also be supported and supplemented by existing subsurface geologic and hydrologic information obtained from the borehole drilling program.