This data set represents the extent of the Rio Grande aquifer system in the states of Colorado, New Mexico, and Texas.

This data set represents the extent of the Basin and Range aquifers in the states of California, Utah, Arizona, and Nevada.

This digital geospatial data set consists of geohydrologic unit boundaries shown in the report "Structure, outcrop, and subcrop of the bedrock aquifers along the western margin of the Denver Basin, Colorado" (Robson and others, 1998).

This data set represents the extent of the Basin and Range carbonate-rock aquifers in the states of Idaho, Utah, Arizona, Nevada, and California.

These data are in support of report DS 456 (Arnold and others, 2009). This grid represents the depth to groundwater in the High Plains Aquifer in Colorado in 2000. The depth-to-water grid was generated for the entire High Plains Aquifer from depth-to-water measurements collected in 2000. Shown as figure 12 in McMahon and others (2007).

In 2004, the U.S. Geological Survey initiated a large-scale regional study of the Denver Basin aquifer system to evaluate the hydrologic effects of continued pumping and document an updated groundwater-flow model useful for appraisal of hydrologic conditions (Paschke, 2011). This data release includes spatial datasets used as input for a three-dimensional groundwater-flow model of the Denver Basin aquifer system. Spatial datasets were developed for six Denver Basin bedrock aquifers and five intervening confining units including, from oldest to youngest, the Laramie-Fox Hills aquifer (KLF), Laramie confining unit (KLC), lower Arapahoe aquifer (LKA), Arapahoe confining unit (KAC), upper Arapahoe aquifer (UKA), Denver lower confining unit (TKDLC), Denver aquifer (TKD), Denver upper confining unit (TKDUC), lower Dawson aquifer (LTDW), Dawson confining unit (TDWC), and upper Dawson aquifer (UTDW). Maps of the base altitude and lateral extent of each aquifer were developed for the 11 aquifer and confining units to define the hydrogeologic framework for the model. The BasePoints.zip folder contains 11 point shapefiles of the data points for altitude of the base of each bedrock aquifer and confining unit and one shapefile with locations of wells in the Denver Basin having geophysical logs ("PP1770_seo_geologs_points"). The "BaseContours.zip" folder contains 11 polyline shapefiles of generalized lines of equal base altitude for each bedrock aquifer and confining unit derived from the base-altitude points, and the "Extents.zip" folder contains 11 polygon shapefiles representing the extent of each aquifer and confining unit. Maps of silt-plus-sand thickness were developed for the six bedrock aquifers and were used to estimate hydraulic conductivity and specific yield in the groundwater-flow model. The "SandPoints.zip" folder contains six point shapefiles of data points for silt-plus-sand thickness of each bedrock aquifer, and the "SandContours.zip" folder contains six polyline shapefiles of generalized lines of equal silt-plus-sand thickness derived from the silt-plus-sand thickness points. Shapefiles in the zipped folders are named using the abbreviation or name of the aquifer or confining unit as shown on Table A2 of Paschke (2011).

This data set represents the extent of the Volcanic and sedimentary-rock aquifers in the states of Montana, Wyoming, Idaho, Nevada, California, Oregon, and Washington.

This data set represents the extent of the Northern Rocky Mountains Intermontane Basins aquifer system in Montana and Idaho.

This data set represents the extent of the Central Valley aquifer system in California.

This data set represents the extent of the Ada-Vamoosa aquifer in Oklahoma.