1961. Walker, Alfred C. Scale bar lower left corner of map. "Prepared by ALFRED C. WALKER, Geologist, Ohio Division of Water" Map side also contains legend and explanation... Ohio. Division of Water.
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1911. Relief shown by contours and spot heights. Depths shown by soundings. 'Revisions made July 1931.' 'The survey of the river proper was begun July 25... District Engineer Office.