The Hydrogeologic Terranes dataset includes separate polygon and line feature classes. The polygon feature class divides the glaciated United States into seventeen distinct terranes using a geologically based approach. Each terrane contains Quaternary sediment that is derived from a common depositional history and can be characterized by texture and thickness. Delineation of hydrogeologic terranes was based on an interpretation of existing geologic mapping of surficial and Quaternary deposits, and thickness of unconsolidated material. Overall thickness of Quaternary sediment was used to qualitatively rank the generalized complexity of geologic framework in each terrane: "lower" complexity (assigned a terrane code = 1), "moderate" (code = 2), and "higher" complexity (code = 3). Letter designations appended to the numeric codes (e.g., 1A, 3C) differentiate terranes of similar complexity. Two unique areas, where thick, stratified, coarse-grained sediment dominates, were assigned code = 4.
The line feature class of the Hydrogeologic Terranes dataset identifies terrane boundary line types. Possible values are: (1) sediment thickness contrast boundary, (2) major river boundary, (3) maximum extent of glacial ice, and (4) extent of Late Wisconsinan glacial ice.