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Data Release for Secondary Hydrogeologic Regions of the Conterminous United States


Publication Date


Belitz, K., Watson, E., Johnson, T.D., and Sharpe, J.B., 2018, Data release for secondary hydrogeologic regions of the conterminous United States: U.S. Geological Survey data release,


The U.S. Geological Survey (USGS) previously identified 62 Principal Aquifers (PAs) in the U.S., with 57 located in the conterminous states. The USGS characterized areas outside of PAs as “other rocks;” other rocks account for about 40% of the area of the conterminous states. This paper subdivides the large area identified as other rocks into Secondary Hydrogeologic Regions (SHRs). SHRs are defined as areas of other rock within which the rocks are of comparable geologic age, lithology, and relationship to the presence or absence of underling PAs or overlying glacial deposits. A total of 69 SHRs were identified. SHRs were identified in two phases. In the first phase, Other Rock Regions (ORRs) were defined as regions underlain by geologic [...]


Attached Files

Click on title to download individual files attached to this item.
“Geodatabase and Metadata”
21.49 MB
“Shapefiles and Metadata”
23.97 MB
“Map showing the 69 Secondary Hydrogeologic Regions of the conterminous U.S.”
5.55 MB
“Maps showing SHRs classified by type, lithology, and geologic province/subprov.”
9.63 MB
“Map showing wells classified by the type of SHR that the well plots within.”
11.62 MB


Identification of Secondary Hydrogeologic Regions in areas outside of Principle Aquifers expands the framework for National assessments.



  • National Water-Quality Assessment Project
  • USGS Data Release Products



Additional Information


Type Scheme Key
DOI doi:10.5066/F7F76BSS

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