Hydrogeologic regions of the conterminous United States

This data release contains shapefiles of hydrogeologic regions of the conterminous United States. The United States Geological Survey (USGS) is developing a National Extent Hydrogeologic Framework. In support of that effort, principal aquifers (PA) (USGS, 2003) and secondary hydrogeologic regions (SHR) (Belitz and others, 2018a) in the conterminous United States were combined into a single dataset referred to as hydrogeologic regions (HR). The dataset reflects the extent of the shallowest HR. Sand and gravel aquifers of alluvial and glacial origin are not included in this data set; the next shallowest HR are shown in these areas. A PA is defined as a regionally extensive aquifer or aquifer system that has the potential to be used as a source of potable (drinkable) water. For study or mapping purposes, aquifers are often combined into aquifer systems. (USGS, 2003). The map of PAs (USGS, 2003) was derived from the Ground Water Atlas of the United States (USGS, 2000). The areas outside the PAs, classified as “other rocks” in the original PA dataset, were subdivided by Belitz and others, 2018a, into SHRs of comparable geologic age, lithology, and relationship to the presence or absence of underlying PAs or overlying glacial deposits. A total of 69 SHRs were identified.

References cited:

Belitz, K., Watson, E., Johnson, T.D., and Sharpe, J., 2018a, Secondary hydrogeologic regions of the conterminous United States: Groundwater, v. 57, no. 3, p. 367-377, accessed June 12, 2025, at https://doi.org/10.1111/gwat.12806.

U.S. Geological Survey, 2000, Ground water atlas of the United States: U.S. Geological Survey Hydrologic Atlas 730, accessed June 12, 2025, at https://doi.org/10.3133/ha730.

U.S. Geological Survey, 2003, Principal aquifers of the 48 conterminous United States, Hawaii, Puerto Rico, and the U.S. Virgin Islands: U.S. Geological Survey data release, accessed June 12, 2025, at https://doi.org/10.5066/P9Y2HOUJ.