| 1. |  | Olney quadrangle, Illinois : 15 minute series (topographic). | Olney (Ill.); Illinois; Maps; Topographic maps; Topography | 1 map : col.; Relief shown by contours and spot heights.; "Culture and drainage in part compiled from aerial photographs taken 1938-1941. Topography by plane-table methods, 1947."; "Contour interval 10... |
