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 <https://pubs.usgs.gov/fs/FS-027-98/fs-027-98.pdf> 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