FIGURE 11.--Maps of eastern South Dakota, to illustrate problems of representing bedrock geology in areas with extensive cover of surficial deposits. A, Surficial, or Quaternary glacial deposits, generalized from Flint (1959). B, Bedrock geology as shown on Geologic Map of the United States. Outcrops of bedrock east of Missouri River are from Geologic Map of South Dakota of 1953; contacts elsewhere, shown by dotted lines, are those shown on the Geologic Map of the United States and are subcrop representations based on subsurface data.