1912. Geological Survey (U.S.). Contour interval 20 feet.;"Surveyed in 1910.";"Surveyed in cooperation with the State of Illinois.";Relief indicated by contours.;1 map, colored;45... Geological Survey (U.S.)|Geological Survey Division (Urbana, Ill.).
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1912. Geological Survey (U.S.). Contour interval 20 feet.;"Surveyed in 1908-1909.";"Surveyed in cooperation with the State of Illinois.";Relief indicated by contours and spot heig... Geological Survey (U.S.)|Geological Survey Division (Urbana, Ill.).
1912. Geological Survey (U.S.). Contour interval 20 feet.;"Surveyed in 1910.";"Surveyed in cooperation with the State of Illinois.";Relief shown by contours and spot heights.;1 ma... Geological Survey (U.S.)|Geological Survey Division (Urbana, Ill.).