The knolls and ridges in this vicinity were formed by deposits of gravel left by the retreating glacier that covered much of Ohio during the Pleistocene Era 10,000 years ago. Popularly known as Devil's Backbones, these ridges can be several miles in length. As the glacier retreated, it also left large round depressions in the earth's surface known as kettles. A kettle was formed by the melting of a buried mass of ice.