| 1. |  | Illinois, Potomac quadrangle. | Potomac (Ill.); Illinois; Maps; Topographic maps; Topography | 1 map : col.; Relief shown by contours and spot heights.; "Surveyed in 1931-1932"; "Contour interval 10 feet"; Shows roadway classification as of 1934.; (W 88⁰00ʹ00ʺ--W 87⁰45ʹ00ʺ/N 40⁰30ʹ00ʺ--N... |
