Clifton Gorge was a refuge in time of trouble for the Shawnee Indians, a barrier to travel for pioneers, and later a source of water power for nineteenth-century industrialists who filled it with mills; today it is protected as part of Ohio's state nature preserve system. The gorge was cut when the last continental ice sheet melted away some 13,000 years ago and a river of meltwater poured south through the area. The exposed bedrock is of Silurian age, deposited on an ocean floor 350 million years ago. Its cliffs are made of dolomite, a calcium carbonate-magnesium rock, and its talus steeps are formed in a layer of easily eroded shale. The narrow gorge, floodplain, and surrounding uplands create a variety of habitats for more than 450 plant species, including several listed as endangered, and this diversity supports an equally interesting animal population only glimpsed by visitors.