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.

Data release containing geospatial data and metadata for select hydrogeologic characteristics of the alluvium in the Lower Arkansas River Valley, Southeast Colorado, 2002, 2008, and 2015. This data release accompanies U.S. Geological Survey Scientific Investigations Map 3378 (https://doi.org/10.3133/sim3378). Geospatial datasets and metadata include: - Rasters showing estimated thickness of the alluvium; fall-to-fall and spring-to-spring water-table altitude change, 2002 to 2008, 2008 to 2015, and 2002 - 2015; and estimated saturated thickness in the alluvium, fall and spring 2002, 2008, and 2015. - Shapefiles showing bedrock contours underlying the alluvium; the outline of the study area and John Martin Reservoir in Bent County, Colorado; well locations and measured water-level altitude in those wells in the fall and spring of 2002, 2008, and 2015. For the purposes of this data release, "fall" is defined as June 1 through November 30, and "spring" is defined as January 1 through May 31 and December 1 through 31 of the same year.

The U.S. Geological Survey in cooperation with the Upper Arkansas Water Conservancy District, created a numerical groundwater-flow model for the Wet Mountain Valley alluvial aquifer using the finite-difference MODFLOW code with the Newton formulation solver. This numerical groundwater-flow model simulates water-budget components, groundwater and surface-water interactions, and evaluates the potential effects of aquifer storage and recovery through an added recharge simulation. The numerical model was spatially discretized into two layers with 261 rows and 133 columns of square cells at 250 meters on each side, for a total of 20,007 active cells. The model was rotated by 36 degrees to the northwest to align with the orientation of the valley and the assumed groundwater-flow directions. The numerical model was temporally discretized into 241 stress periods. The first stress period simulates a mean steady-state period, and the subsequent 240 stress periods were transient and simulate each month from 2000 to 2019. This U.S. Geological Survey data release includes all of the necessary files to simulate the Wet Mountain Valley alluvial aquifer and potential flow paths within it as described in the associated Scientific Investigations Report (https://doi.org/10.3133/sir20245105).

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 dataset was created in support of a study focusing on ground-water 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 ground-water 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 ground water for urban populations, agriculture, and native habitats, the GBCAAS was selected by the U.S. Geological Survey (USGS) Water Resources program as part of the National Water Census Initiative to evaluate the Nation's ground-water availability. These data are derived from the Basin Characterization Model (BCM). The BCM is a distributed-parameter, water-balance accounting model that is run on a monthly time step. The BCM incorporates spatially distributed parameters (monthly precipitation, monthly minimum and maximum air temperature, monthly potential evapotranspiration, soil-water storage capacity, and saturated hydraulic conductivity of bedrock and alluvium) to determine where excess water is available in a basin and whether the excess water is stored in the soil or infiltrates downward into underlying bedrock. This dataset is composed of three raster layers. Two of the layers are outputs of the BCM model, one is an input. The layers are as follows: 1. Estimated average in-place recharge for the years 1940 to 2006 in the GBCAAS study area. In-place recharge is output from the BCM and is calculated as the annual mean amount of water that can drain from the soil zone directly into consolidated bedrock or unconsolidated deposits. 2. Estimated average runoff for the years 1940 to 2006 in the GBCAAS study area. Estimated runoff is output from the BCM and is calculated as the annual mean amount of water that runs off the mountain front or becomes streamflow. 3. Estimated saturated hydraulic conductivity (K) of bedrock and unconsolidated basin fill in the GBCAAS study area. The data are input to the BCM model as one of two temporally invariable inputs: storage capacity of soil and saturated hydraulic conductivity (Flint and Flint, 2007). The dataset was developed by applying assumed K values to geologic formations derived from 1:500,000-scale and 1:750,000-scale digital State geologic maps covering the study area. Hydraulic conductivity estimates of bedrock are uncertain because of the unknown hydraulic properties and spatial distributions of fractures, faults, fault gouge, and shallow infilling materials associated with different bedrock types and evaporative demand. These data are output from a model and should be used with caution. Refer to the larger work citation for details about the data and adjustments made to estimated recharge and runoff in water balance calculations made for the GBCAAS study. References cited: Flint, A.L., and Flint, L.E., 2007, Application of the Basin Characterization Model to estimate in-place recharge and runoff potential in the Basin and Range carbonate-rock aquifer system, White Pine County, Nevada and adjacent areas in Nevada and Utah: U.S. Geological Survey Scientific Investigations Report 2007-5099, 30p.

This digital dataset defines the extent of the alluvial deposits in the Central Valley of California and encompasses the contiguous Sacramento, San Joaquin, and Tulare Lake groundwater basins defined by California's Department of Water Resources. The boundary encompasses an approximate 50,000 square-kilometer region of California. The boundary was used to define the lateral boundary of the area simulated by the transient Central Valley Hydrologic Model (CVHM) (Faunt, 2009). 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 its 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 contains 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). The study area is characterized by north-south trending alluvial basins separated by intervening mountain ranges. HA boundaries generally coincide with the topographic highs separating these basins but may also contain arbitrary divisions that have no topographic control. HAs generally consist of thick layers of unconsolidated geologic deposits in the basins and consolidated bedrock in the mountain ranges. The basins are underlain by bedrock at varying depths. Much of the bedrock in the study area consists of permeable carbonate and volcanic rock strata, both of which allow some degree of hydraulic connection between hydrographic areas. The hydrographic area boundaries in this dataset have been assigned a code identifying each boundary as a potential barrier, conduit, or neutral zone to groundwater flow between basins. References cited: Buto, S.G., 2009, Digital representation of 1:1,000,000-scale Hydrographic Areas of the Great Basin: U.S. Geological Survey Digital Data Report 457, 5 p., Harrill, J.R., Gates, J.S., and Thomas, J.M., 1988, Major ground-water flow systems in the Great Basin region of Nevada, Utah, and adjacent states: U.S. Geological Survey Hydrologic Investigations Atlas HA-694-C, 2 sheets, scale 1:1,000,000.

This data release contains environmental tracer model inputs, outputs, and model results. Dataset includes environmental tracer concentrations, simulated recharge conditions (water temperature, excess air), and estimated groundwater residence times. This dataset supports an integrated hydrologic investigation of groundwater recharge processes and groundwater flow in the Wet Mountain Valley alluvial aquifer, Custer and Fremont Counties, Colorado. Data were collected by the U.S. Geological Survey in cooperation with the Upper Arkansas Water Conservancy District.

This data set represents the extent of the Pecos River Basin alluvial aquifer in New Mexico, and Texas.