Geologic Overview, Description of Map Units, and Correlation Chart for the Surficial Geologic Materials Maps of the Letts Quadrangle, Iowa and the Blanchard Island Quadrangle, Illinois - Iowa, December 1994

(1994) Geologic Overview, Description of Map Units, and Correlation Chart for the Surficial Geologic Materials Maps of the Letts Quadrangle, Iowa and the Blanchard Island Quadrangle, Illinois - Iowa, December 1994. University of Iowa

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Abstract

The Letts, Iowa and Blanchard Island, Illinois-Iowa 1:24,000-scale geologic quadrangles cover an area from 41° 15' to 41° 22' 30" N latitude and 91° to 91° 15' W longitude. The area encompasses two geomorphic regions: 1) loess-mantled uplands of central eastern Iowa and central western Illinois, and 2) the Mississippi River Valley. Prior geologic mapping in the area consists of mapping of the Des Moines 4° X 6° Quadrangle at a scale of 1:1,000,000 (Hallberg et al., 1991) and 1:100,000-scale landform maps produced for cultural resource surveys in the Mississippi River Valley (Benn et al., 1988). The latter use a mixture of lithologic and chronologie units and do not define map units using formal stratigraphic procedures.