The bedrock beneath Ohio is from the Paleozoic Era. It ranges in age from the Ordovician to the Permian (approximately 450 to 290 million years old; Ohio Geological Map [pdf]). In much of the state, sediments deposted during the Pleistocene Glacial Epoch covers the bedrock; Ohio Glacial Map [pdf]. The oldest rocks in Ohio are in the southwetern corner of the state. Ohio bedrock is folded into the Cincinnati Arch that extends from Hamilton County (southwest) to Ottawa County (north-central). From the axis of this arch, surface bedrock becomes younger toward the northwest toward the Michigan Basin and toward to east and southeast toward the Appalachian Basin. For additonal information about the Ohio geology, consult the Division of Geologic Survey at the Ohio Department of Natural Resources.
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