| 1. |  | Illinois, Orion quadrangle. | Orion (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 by Air Corps, U.S. Army."; "Surveyed in 1930-1932"; "Contour interval 20 feet."... |
