Base source: USGS 1:100,000 county base map compiled in 1975; interpretations derived from soil map constructed 1974.; "Projection and 10,000-metre grid ticks, zone 15: Universal Transverse Mercator."; "25,000-foot grid ticks based in Illinois coordinate system, west zone."; June 1977.; Includes location map. 92 x 122 centimeters Scale 1:50,000