1 map ; 51 x 70 cm
"Soundings are in feet and tenths of a foot."
"The figures on land express the elevations above the lake surface in feet and decimals. The horizontal curves or contour lines are drawn at intervals of 5 feet of perpendicular elevation."
"Accompanying Lt. Colonel Graham's annual report (no. 200) to the Chief Top. Engineer, dated Chicago September 30th 1857."
"Map G no. 50."
Graham, J. D. (James Duncan), 1799-1865, Mayer, J. R. (John R.), and United States. Army. Corps of Topographical Engineers