BEDROCK-TOPOGRAPHY AND DRIFT-THICKNESS MAPS FOR OHIO

The Ohio Department of Natural Resources, Division of Geological Survey recently released two new map products, Shaded bedrock-topography map of Ohio and, Shaded drift-thickness map of Ohio. Both maps have accompanying texts and figures, and are available in full-color, 1:500,000 scale, print-on-demand format and as GIS files on CD. Glacially derived material up to 720 feet thick covers the bedrock surface in the northern and western two-thirds of Ohio. These maps and accompanying digital datasets provide information on bedrock-surface elevation and drift thickness that is essential for many environmental, land-use planning, engineering, and geotechnical applications. The Shaded bedrock-topography map of Ohio is a digital compilation of bedrock-topography contours and associated data points from 788 1:24,000-scale, open-file bedrock-topography maps originally prepared for construction of a new bedrock-geology map of Ohio. The bedrock-topography map uses color ramping to clearly display topographic relief on the bedrock surface including the steep-sided buried valleys in western Ohio caused by dissection associated with the Teays Valley System, and the smooth bedrock surface of northwest Ohio associated with the movement of glacial ice out of the Erie Basin. The Shaded drift-thickness map of Ohio is a computer-generated derivative product created by subtracting bedrock-surface elevations from land-surface elevations derived from National Elevation Dataset. The drift-thickness map clearly shows glacial features where deposits thicken such as in the case of moraines, kames, and eskers. It also shows the extent of thick fill associated with buried valleys throughout glaciated Ohio and areas of thick outwash and lacustrine deposits in valleys beyond the glacial margin. The maps also shows that drift across large expanses of glaciated Ohio is commonly less than 50 feet thick and that drift greater than 200 feet thick is generally confined to areas over filled or partially filled buried valleys.