This digital dataset contains the 9 major areas used to subdivide the Central Valley for the interpolation of the percentage of coarse-grained deposits into the texture model. This texture model was used as input data for the hydraulic properties portion of the Central Valley Hydrologic Model (CVHM). The Central Valley encompasses an approximate 50,000 square-kilometer region of California. The complex hydrologic system of the Central Valley is simulated using the USGS numerical modeling code MODFLOW-FMP (Schmid and others, 2006). This simulation is referred to here as the CVHM (Faunt, 2009). Utilizing MODFLOW-FMP, the CVHM simulates groundwater and surface-water flow, irrigated agriculture, land subsidence, and other key processes in the Central Valley on a monthly basis from 1961-2003. The total active modeled area is 20,334 square-miles on a finite difference grid comprising 441 rows and 98 columns. Slightly less than 50 percent of the cells are active. The CVHM model grid has a uniform horizontal discretization of 1x1 square mile and is oriented parallel to the valley axis, 34 degrees west of north (Faunt, 2009). In order to better characterize the aquifer-system deposits, lithologic data from approximately 8,500 drillers' logs of boreholes ranging in depth from 12 to 3,000 feet below land surface were compiled and analyzed. The percentage of coarse-grained sediment, or texture, then was computed for each 50-foot depth interval of the drillers' logs. A 3-dimensional texture model was developed by interpolating the percentage of coarse-grained deposits onto a 1-mile spatial grid at 50-foot-depth intervals from land surface to 2,800 feet below land surface. The CVHM is the most recent regional-scale model of the Central Valley developed by the U.S. Geological Survey (USGS). The CVHM was developed as part of the USGS Groundwater Resources Program (see "Foreword", Chapter A, page iii, for details).

Boundary of the alluvium in the Lower Arkansas River Valley, Southeast Colorado. Boundary defined by extent of available bedrock information and geologic maps. Also includes approximate shoreline of John Martin Reservoir in Bent County, Colorado. Scale of maps used for digitization was 1:62,500. All digitization and geoprocessing was done using ArcGIS Desktop v10 (Environmental Systems Research Institute, 2011)

SWPA_alvbsn is a vector dataset of alluvial-fill basin statistics for the Southwest United States. Statistics for each basin include physical details such as area, landcover, elevation, slope and precipitation. Anthropogenic data for basin include landuse, population, and wateruse.

This dataset contains the amalgamation of the hydrographic area (HA) boundaries and polygons for the GBCAAS study area. The study area consists of 165 HAs based on Great Basin HAs defined by the USGS in 1988 (Harrill and others, 1988; Buto, 2009). This dataset does not contain the HA boundaries or geologic details included in the source dataset. For that information, please see the metadata for the source dataset at https://water.usgs.gov/GIS/metadata/usgswrd/XML/sir2010_5193_ha1000.xml The study area boundary dataset is used by the Office of Groundwater, U.S. Geological Survey, in its hyrogeological framework website.

This digital dataset defines the spring 1961 water-table altitude for the California's Central Valley. It was used to initiate the water-level altitudes for the upper zones of the transient hydrologic model of the Central Valley flow system. The Central Valley encompasses an approximate 50,000 square-kilometer region of California. The complex hydrologic system of the Central Valley is simulated using the USGS numerical modeling code MODFLOW-FMP (Schmid and others, 2009). This simulation is referred to here as the Central Valley Hydrologic Model (CVHM) (Faunt, 2009). Utilizing MODFLOW-FMP, the CVHM simulates groundwater and surface-water flow, irrigated agriculture, land subsidence, and other key processes in the Central Valley on a monthly basis from 1961-2003. The starting heads are based on the water-table and potentiometric surface developed by Williamson and others (1989). Maps of the spring 1961 water-table and hydraulic head in the lower pumped zone are shown in Figure 31 of Williamson and others (1989). The CVHM is the most recent regional-scale model of the Central Valley developed by the U.S. Geological Survey (USGS).The CVHM was developed as part of the USGS Groundwater Resources Program (Faunt, 2009. See "Foreword", Chapter A, page iii, for details).

This raster dataset represents the boundaries of the hydrogeologic areas of the Southwest Principal Aquifer (SWPA) study of the National Water Quality Assessment (NAWQA) program. It is a compilation of the pre-existing Hydrogeologic Areas of the Southwest Ground-Water Resources Project, with additional data from the Central and Coastal basins of California, Northern New Mexico Rio Grande Valley, and South Central Colorado San Luis Valley.

This digital dataset contains the monthly diversions from the surface-water network for the Central Valley Hydrologic Model (CVHM). The Central Valley encompasses an approximate 50,000 square-kilometer region of California. The complex hydrologic system of the Central Valley is simulated using the USGS numerical modeling code MODFLOW-FMP (Schmid and others, 2006). This simulation is referred to here as the CVHM (Faunt, 2009). Utilizing MODFLOW-FMP, the CVHM simulates groundwater and surface-water flow, irrigated agriculture, land subsidence, and other key processes in the Central Valley on a monthly basis from 1961-2003. The total active modeled area is 20,334 square-miles. The CVHM includes complex surface-water management processes. The hydrology of the present-day Central Valley and the CVHM model are driven by surface-water deliveries and associated groundwater pumpage. The Streamflow Routing Package (SFR1) is linked to MODFLOW-FMP to facilitate the simulated conveyance of surface-water deliveries. If surface-water deliveries do not meet the farm-delivery requirement, the FMP invokes simulated groundwater pumping to meet the demand. The surface-water network represents a subset of the entire stream network in the valley. Even so, it covers about 3,000 kilometers of surface-water and is simulated using 208 stream segments that represent 2244 stream reaches, with 43 inflows and 66 diversion locations providing 64 routed and 41 non-routed deliveries. Most of these inflows are regulated by dams and most of the deliveries are conveyed through an extensive canal network. The routed deliveries are conveyed through the simulated surface-water network, while the non-routed delivery conveyance typically occurs through small canals or diversion ditches and are not directly simulated. Much of the surface-water diversion and delivery information was compiled by the California Department of Water Resources (DWR) for 21 water-balance subregions (WBSs) covering the valley floor (C. Brush, California Department of Water Resources, written commun., February 21, 2007). The CVHM is the most recent regional-scale model of the Central Valley developed by the U.S. Geological Survey (USGS). The CVHM was developed as part of the USGS Groundwater Resources Program (see "Foreword", Chapter A, page iii, for details).

This dataset was created in support of a U.S. Geological Survey (USGS) study focusing on groundwater resources in the Great Basin carbonate and alluvial aquifer system (GBCAAS). The GBCAAS is a complex aquifer system comprised of both unconsolidated and bedrock formations covering an area of approximately 110,000 square miles. The aquifer system is situated in the eastern portion of the Great Basin Province of the western United States. The eastern Great Basin is experiencing rapid population growth and has some of the highest per capita water use in the Nation. These factors, combined with the arid setting, have levied intensive demand upon current groundwater resources and, thus, predictions of future shortages. Because of the large regional extent of the aquifer system, rapid growth in the region, and the reliance upon groundwater for urban populations, agriculture, and native habitats, the GBCAAS was selected by the USGS Water Resources program as part of the National Water Census Initiative to evaluate the Nation's groundwater availability. This dataset consists of potentiometric contours, control points used to guide the creation of the contours, and a grid of 2 square-mile cells used to average the water-level value of selected control points. Control points are based on water-level measurements at well and spring locations from the USGS National Water Information System (NWIS, Mathey, 1998). Additional control points were derived from estimates of water-level altitudes in perennial mountain streams based on National Hydrography Dataset (NHD, 1999) stream reaches. References cited: Mathey, Sharon B., ed., 1998, National Water Information System (NWIS): U.S. Geological Survey Fact Sheet 027-98, 2 p., Accessed January 14, 2009 at U.S. Geological Survey, 1999, National Hydrography Dataset: U.S. Geological Survey Fact Sheet 106-99, accessed March 2007 at http://erg.usgs.gov/isb/pubs/factsheets/fs10699.html

This digital dataset contains monthly reference evapotranspiration (ETo) data for the Central Valley Hydrologic Model (CVHM). The Central Valley encompasses an approximate 50,000 square-kilometer region of California. The complex hydrologic system of the Central Valley is simulated using the USGS numerical modeling code MODFLOW-FMP (Schmid and others, 2006b). This simulation is referred to here as the CVHM (Faunt, 2009). Utilizing MODFLOW-FMP, the CVHM simulates groundwater and surface-water flow, irrigated agriculture, land subsidence, and other key processes in the Central Valley on a monthly basis from 1961-2003. The total active modeled area is 20,334 square-miles on a finite-difference grid comprising 441 rows and 98 columns. Slightly less that 50 percent of the cells are active. The CVHM grid has a uniform horizontal discretization of 1x1 square mile and is oriented parallel to the valley axis, 34 degrees west of north (Faunt, 2009). The main climatic contributors to the CVHM are ETo and precipitation. Data from Parameter-Elevation Regressions on Independent Slopes Model (PRISM) (Climate Source, 2006) provide the temperature and precipitation on a monthly basis for a 2-kilometer grid. Mapping land-use type and distribution is integral to calculating the crop irrigation demand and, ultimately, the water use in the Central Valley. For a given land use, the demand can be calculated from two variables: crop coefficient (Kc) and reference evapotranspiration (ETo). For the CVHM, ETo is calculated from the daily minimum and maximum air temperatures derived from PRISM data and the extraterrestrial solar radiation (Faunt, 2009, p. 151). The CVHM is the most recent regional-scale model of the Central Valley developed by the U.S. Geological Survey (USGS). The CVHM was developed as part of the USGS Groundwater Resources Program (see "Foreword", Chapter A, page iii, for details).