A NEW COMPILATION SURFICIAL GEOLOGIC MAP OF THE SOUTHERN DRIFTLESS AREA, SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS, AND A MOVE AWAY FROM GEOLOGIC MAPS DELINEATED BY COLONIAL BOUNDARIES

The Wisconsin Geological & Natural History Survey (WGNHS) is compiling a new 1:250,000-scale map of the surficial geology of the southern portion of the unglaciated Driftless Area of southwest Wisconsin and northwest Illinois. This involves streamlining and simplifying available 1:100,000-scale surficial geologic maps and the addition of new mapping at the same level of detail where none is available.

Traditionally, 1:100,000-scale mapping projects at the WGNHS have been identified, proposed, and funded based on county boundaries. This new compilation map includes all or parts of eight previously mapped counties, parts of four counties that are currently being mapped, and parts of two unmapped counties. Rather than adhering to colonial boundaries, though, the boundaries of this compilation map will be delineated by physiographic and geomorphic features: the maximum extents of pre-Illinoian, Illinoian, and Wisconsin glaciations; the Black River in western Wisconsin; and the transition from fluvially-incised Paleozoic strata typical of the Driftless Area to the Central Sand Plain that represents the former bed of glacial Lake Wisconsin.

Delineating maps based on arbitrary boundaries such as counties can be efficient from the standpoint of funding and publishing. However, a move—when appropriate—to physiographic/geomorphic boundaries for surficial geologic maps can provide the opportunity to convey a more nuanced, fully-formed, and targeted geologic story on the map. This sentiment dovetails with on-going efforts by the WGNHS to develop strong, respectful relationships with the Native American tribe and nations of Wisconsin, which will hopefully lead to collaborative opportunities to publish surficial geologic maps in the future with boundaries and base layers that are culturally relevant to the tribes and nations.