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.