INTEGRATED HYDROGEOLOGIC FRAMEWORK MODEL FOR TWO GROUNDWATER BASINS AT FORT IRWIN NATIONAL TRAINING CENTER IN THE MOJAVE DESERT, CALIFORNIA

Surficial and subsurface mapping of hydrogeoloic layers is an important component to developing a comprehensive understanding of the groundwater system. As part of a broader hydrologic investigation of the Fort Irwin National Training Center (NTC), a simplified hydrogeologic framework model is being constructed for two adjacent groundwater basins, Superior and Goldstone. These basins are located in the western-most section of Fort Irwin NTC and include portions of land owned by the Bureau of Land Management and China Lake Naval Air Station. Previous hydrogeologic studies conducted by the U.S. Geological Survey (USGS) in Fort Irwin NTC have characterized the surficial geology of the basins and identified major through-going faults by the construction of geologic maps and cross-sections. This characterization has been done by examination of newly drilled multiple-completion monitoring wells, analysis of gravity measurements for depth-to-crystalline basement, and a series of airborne electromagnetic (AEM) surveys. A limited number of boreholes were drilled in the study area; therefore, the majority of subsurface lithostratigraphic information is derived from geologic cross-sections and resistivity values calculated from the AEM surveys. From this suite of information, a 3D hydrogeologic framework model was developed by using Earthvision¹. The datasets are uploaded into Earthvision as gridded surfaces, or surfaces in cross-section, and used to extrapolate the subsurface extent of four major lithostratigraphic units: 1) Bmt – Mesozoic metamorphic and plutonic crystalline basement; 2) Tv – Tuffaceous and volcaniclastic Miocene deposits; 3) Tf – Miocene mafic-felsic lava flows and domes; 4) Qa - Quaternary sediments. The primary groundwater-producing unit is Tv. AEM resistivity zones are calibrated to the regional geology by using surficial maps and known geologic structures. In general, Bmt and Tf are highly resistive, Qa is moderately resistive/conductive, and Tv is highly to moderately conductive. Our AEM survey data is consistent with known geologic structures and, in combination with geologic cross sections and surficial geology, allows for a reasonable interpretation of the subsurface lithostratigraphy.

¹ For information only, does not constitute endorsement or warranty by the USGS