Mouth of South Black River, Michigan from survey made in August 1856 by assistant John R. Mayer, under the direction of Brevet Lieut. Col. J.D. Graham, Major, U.S. Top. Engineers. Superintending Engineer of Lake Michigan Works.
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."; 1 map 51 x 70 c
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