This data set represents the extent of the California Coastal Basin aquifers in California.

This data set represents the extent of the Northern California volcanic-rock aquifers in California.

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

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 Basin and Range carbonate-rock aquifers in the states of Idaho, Utah, Arizona, Nevada, and California.

This data set represents the extent of the Southern Nevada volcanic-rock aquifers in Nevada.

This data set represents the extent of the Texas coastal uplands aquifer system in Texas.

This geodatabase includes spatial datasets that represent the Central Valley aquifer system in the State of California. Included are: (1) polygon extents; datasets that represent the aquifer system extent, the entire extent subdivided into subareas or subunits, (2) raster datasets for the altitude of each aquifer subarea or subunit, (3) altitude, and thickness contours used to generate the surface rasters, (4) georeferenced images of the figures that were digitized to create the altitude or thickness contours. The images and digitized contours are supplied for reference. The extent of the Central Valley aquifer system is from the spatial dataset of the USGS Professional Paper 1766 (USGS PP 1766) alluvial aquifer extent - modified to make internal areas where the aquifer is not present equal to "Null" - and was referenced to a digital version of the aquifer extent presented in the Groundwater Atlas of the United States (the U.S. Geological Survey Hydrologic Atlas 730-B (USGS HA 730-B). The Central Valley aquifer system has two aquifer subunits, in order from the most surficial to the deepest: A1: continental deposits, A2: marine deposits. The altitude and thickness contours for each subunit were digitized from georeferenced figures of altitude contours in U.S. Geological Survey Professional Paper 1401-D (USGS PP 1401-D), and U.S. Geological Survey Open File Report 95-96 (USGS OFR 95-96). The resultant top and bottom altitude values were interpolated into surface rasters with a GIS using tools that create hydrologically correct surfaces from contour data, deriving the altitude from the thickness (depth from the land surface). The primary tool was a version of "Topo to Raster" used in ArcGIS, ArcMap, Esri 2014.

The Central Valley, and particularly the San Joaquin Valley, has a long history of land subsidence caused by groundwater development. The extensive withdrawal of groundwater from the unconsolidated deposits of the San Joaquin Valley lowered groundwater levels and caused widespread land subsidence—reaching 9 meters by 1981. More than half of the thickness of the aquifer system is composed of fine-grained sediments, including clays, silts, and sandy or silty clays that are susceptible to compaction. In an effort to aid water managers in understanding how water moves through the aquifer system, predicting water-supply scenarios, and addressing issues related to water competition, the United States Geological Survey (USGS) developed a new hydrologic modeling tool, the Central Valley Hydrologic Model (CVHM; Faunt and others 2009). The data presented in this data release will be used to facilitate updates to the original CVHM, and represent aquifer-system compaction observations (measurements) using borehole extensometer data during 1958–2018 by USGS, California Department of Water Resources, San Luis and Delta-Mendota Water Agency, and Luhdorff and Scalmanini Consulting Engineers. For a more detailed description of borehole extensometer methods, please see Sneed and others (2013; 2018).