EDMAP-SPONSORED GEOLOGIC MAPPING IN THE BLACK HILLS DEVELOPMENT CORRIDOR, SOUTH DAKOTA

The EDMAP program of the US Geological Survey has supported four graduate student theses at South Dakota School of Mines and Technology involving preparation of 7.5-minute geologic maps (Blackhawk, Hayward, Hermosa, and Silver City) in the Black Hills Development Corridor. These maps have been, or will be, published in digital format by the South Dakota Geological Survey as part of a larger study by SDSMT, SDGS, and the West Dakota Water Development District that examines the geology, geologic hazards, ground water, and geologic resources of this rapidly urbanizing area along the eastern flank of the Black Hills uplift.

As a group, these quadrangles are underlain by complexly deformed Proterozoic metamorphic and igneous rocks, a gently east-dipping section of Cambrian through Cretaceous continental and marine strata (deformed by Laramide age folds), and the unconformably overlying Tertiary White River Group. The geologic maps serve as a base for additional maps relating to: aquifer vulnerability for the Madison and Minnelusa aquifers; geologic hazards relating to slope stability on Mesozoic shale and sandstone, flood plains (e.g., Rapid Creek), and solution collapse features (gypsum in Triassic redbeds); structural interpretations using structural contours; and economic resources, especially concerning industrial minerals (limestone, gypsum, sand and gravel). Fracture data taken during the mapping are useful in regard to secondary porosity in both the Precambrian basement and Paleozoic aquifers and in structural studies related to Laramide doming.