| 1. |  | Walnut quadrangle, Illinois : 15 minute series (topographic) | Maps; Topographic maps; Topography; Illinois; Walnut (Ill.) | 1 map : col.; Relief shown by contours and spot heights.; "Culture and drainage in part compiled from aerial photographs taken 1937, 1939 and 1941. Topography by plane-table methods, 1947."; "Contour interval... |
