This map is a product of the Black Hills Hydrology Study, which was initiated in 1990 to assess the quantity, quality, and distribution of surface water and ground water in the Black Hills area of South Dakota (Driscoll, 1992). This long-term study is a cooperative effort between the U.S. Geological Survey (USGS), the South Dakota Department of Environment and Natural Resources, and the West Dakota Water Development District, which represents various local and county cooperators. This map is part of a series of 1:100,000-scale maps for the study. The maps include a hydrogeologic map, structure-contour maps (altitudes of the tops of formations) for five formations that contain major aquifers in the study area, and potentiometric maps for these five major aquifers (the Inyan Kara, Minnekahta, Minnelusa, Madison, and Deadwood aquifers).
The study area consists of the topographically defined Black Hills and adjacent areas located in western South Dakota. The Black Hills area is an elongated, dome-shaped feature, about 125 miles long and 60 miles wide, which was uplifted during the Laramide orogeny (Feldman and Heimlich, 1980). The oldest geologic units in the study area are Precambrian metamorphic and igneous rocks, which are exposed in the central core of the Black Hills. Surrounding the Precambrian core is a layered series of sedimentary rocks including limestones, sandstones, and shales that are exposed in roughly concentric rings around the uplifted flanks of the Black Hills. The bedrock sedimentary units typically dip away from the uplifted Black Hills at angles that approach or exceed 10 degrees near the outcrops, and decrease with distance from the uplift. Many of the sedimentary units contain aquifers, both within and beyond the study area. Recharge to these aquifers occurs from infiltration of precipitation upon the outcrops and, in some cases, from infiltration of streamflow (Hortness and Driscoll, 1998). Artesian conditions generally exist within these aquifers where an upper confining layer is present. Flowing wells and artesian springs that originate from confined aquifers are common around the periphery of the Black Hills.
The purpose of this map is to show the altitude of the top (structure contours) of the Minnekahta Limestone within the area of the Black Hills Hydrology Study. The depth to the top of the Minnekahta Limestone can be estimated at a specific site by subtracting the altitude of the top of the formation from the topographic elevation. However, caution is urged in determining the depth to the top of the formation in areas on the map where the contours are approximately located.
The outcrops shown on the map are from Strobel and others (1999), and the structural features are modified from Redden (1994) and Strobel and others (1999). The data points shown on this map were compiled from interpretation of drillers' logs and geophysical logs of water wells and oil, gas, and water test holes, and from information stored in the ground-water database of the USGS National Water Information System. Many of the site locations were field verified during the study. The altitudes of subsurface contacts were data compiled by J. Paul Gries (South Dakota School of Mines and Technology), the South Dakota Geological Survey, and the USGS. In some areas, data were either unavailable or insufficient to adequately determine the depth to the top of the Minnekahta Limestone, even though information about deeper formations was available and was used for other maps of this series. Additional information for the wells and test holes used for this map are presented in Carter (1999). In areas where no wells penetrated the Minnekahta Limestone, the altitude of the top of the formation was estimated based on the structure contours on top of the shallower Inyan Kara Group (Carter and Redden, 1999). The structure contours in these areas probably are less accurate than in areas nearer the outcrop of the Minnekahta Limestone.
The Permian-age Minnekahta Limestone is a fine-grained, purple to gray laminated limestone (Strobel and others, 1999), which forms a prominent dip slope outcrop around the Black Hills uplift. The thickness of the Minnekahta Limestone ranges from 25 to 65 feet in the study area (Strobel and others, 1999). The Minnekahta Limestone is overlain by red beds of the Permian- and Triassic-age Spearfish Formation and underlain by the Permian-age Opeche Shale; hence, the Minnekahta Limestone can be readily identified in well cuttings and probably is the most accurate subsurface datum available.
The Minnekahta Limestone generally dips away from the core of the Black Hills. The dip of the top of the Minnekahta Limestone generally is steepest near the outcrop, where it can exceed 20 degrees, and gradually decreases with increasing distance from the outcrop to less than 1 degree near the study area boundary. The altitude of the top ranges from 4,900 feet above sea level (based on the National Geodetic Vertical Datum of 1929) in the southwestern part of the study area to 1,400 feet below sea level in the northeastern part of the study area.
Carter, J.M., 1999, Selected data for wells and test holes used in structure-contour maps of the Inyan Kara Group, Minnekahta Limestone, Minnelusa Formation, Madison Limestone, and Deadwood Formation: U.S. Geological Survey Open-File Report 99-260, 51 p.
Carter, J.M., and Redden, J.A., 1999, Altitude of the top of the Inyan Kara Group in the Black Hills area, South Dakota: U.S. Geological Survey Hydrologic Investigations Atlas HA-744-A, 2 sheets, scale 1:100,000.
Driscoll, D.G., 1992, Plan of study for the Black Hills Hydrology Study, South Dakota: U.S. Geological Survey Open-File Report 92-84, 10 p.
Feldman, R.M., and Heimlich, R.A., 1980, The Black Hills: K/H Geology Field Guide Series, Kendall/Hunt Publishing Company, Kent State University, Kent, Ohio, 190 p.
Hortness, J.E., and Driscoll, D.G., 1998, Streamflow losses in the Black Hills of western South Dakota: U.S. Geological Survey Water-Resources Investigations Report 98-4116, 99 p.
Redden, J.A., 1994, Structural contours and Phanerozoic structures in the Rapid City and Mount Rushmore, South Dakota 1:100,000 scale quadrangles: U.S. Geological Survey Open-File Report 95-81, 4 sheets, scale 1:100,000.
Strobel, M.L., Jarrell, G.J., Sawyer, J.F., Schleicher, J.R., and Fahrenbach, M.D., 1999, Distribution of hydrogeologic units in the Black Hills area, South Dakota: U.S. Geological Survey Hydrologic Investigations Atlas HA-743, 3 sheets.
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Sheet 1 of 2 (PDF, 9.2MB), Northern part of area | Sheet 2 of 2 (PDF, 11.3MB), Southern part of area
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Send questions or comments about this report to J.M. Carter (605) 355-4560 ext. 215.
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