Gravity anomaly contours. Contour interval, 2 mGal. Hachures indicate gravity low. Contours were computergenerated based on a 300-m grid. Although the data have been edited, caution should be exercised when interpreting anomalies controlled by only a single gravity station.

The Spring and Snake Valleys area of Nevada and Utah are two of the major groundwater recharge areas in the eastern part of the Great Basin that were investigated in order to characterize the geophysical framework of the region. Although gravity coverage was extensive over parts of the study area, data were sparse for much of Spring Valley. We addressed this lack of data by establishing of five hundred and forty-five new gravity stations in the region. All available gravity data for the study area were then evaluated to determine their reliability, prior to calculating an isostatic residual gravity map of the area that can be used for subsequent analyses. A gravity inversion method was used to calculate depths to pre-Cenozoic basement rock and estimates of maximum alluvial/volcanic fill in the major valleys of the study area. The enhanced gravity coverage and the incorporation of lithologic information from several deep oil and gas wells yields a much improved view of subsurface shapes of these basins and will provide insights useful for the development of hydrogeologic models for the region.

No abstract

Cenozoic basins in eastern Nevada and western Utah constitute major groundwater recharge areas in the eastern part of the Great Basin and these were investigated to characterize the geologic framework of the region. Prior to these investigations, regional gravity coverage was variable over the region, adequate in some areas and very sparse in others. Cooperative studies described herein have established 1,447 new gravity stations in the region, providing a detailed description of density variations in the middle to upper crust. All previously available gravity data for the study area were evaluated to determine their reliability, prior to combining with our recent results and calculating an up-to-date isostatic residual gravity map of the area. A gravity inversion method was used to calculate depths to pre-Cenozoic basement rock and estimates of maximum alluvial/volcanic fill in the major valleys of the study area. The enhanced gravity coverage and the incorporation of lithologic information from several deep oil and gas wells yields a much improved view of subsurface shapes of these basins and provides insights useful for the development of hydrogeologic models for the region.

No abstract