1. Quaternary geologic map of the Dakotas 4⁰ x 6⁰ quadrangle, United States Yale Public content 1995. 2002-06-01T04:00:00Z. 2002-06-01T04:00:00Z. Geological Survey (U.S.). The Survey ; For sale by Map Distribution. English. Public. North Dakota, South Dakota, and Minnesota. Quaternary.