From Ohio History Central
View of the Glacial Grooves on the north side of Kelley's Island, Ohio, ca. 1930-1960.
In respect to Ohio, glaciation refers to several advances of continental glaciers that covered up to two-thirds of the state beginning about two million years ago during the Pleistocene Epoch. The last of these glaciers left Ohio about 14,000 years ago. It is estimated that at the height of a glacial advance, ice was a mile thick in the Erie basin and 1,000 feet thick in central Ohio in the Columbus area. These glaciations greatly modified the landscape of Ohio and left rich agricultural soils and valuable deposits of sand and gravel and clay.