This coverage contains information about the buried valleys within the Standing Rock Indian Reservation, Sioux County, North Dakota, and Corson County, South Dakota. The delineation of the buried valleys was included as part of the surficial geology map (figure 5) created by Howells (1982). The digital data were produced by the U.S. Geological Survey (USGS) in cooperation with the U.S. Environmental Protection Agency. Figure 5 in Howells (1982) was scanned and digitized on-screen to create this coverage. See cross reference information for more detail. According to the map credit for figure 5, the geology for Sioux County was based on soil maps prepared by the U.S. Bureau of Indian Affairs (1959), data collected by Randich (1975), and a geologic map by Carlson (1978). The geology for Corson County was based on soil maps prepared by the U.S. Bureau of Indian Affairs (1959) and unpublished maps of the U.S Soil Conservation Service, modified by test drilling and field reconnaissance.