Glaciers reshaped Ohio by filling valleys, wearing down hills, and turning rock to dust. Although the ice did not extend over all of Ohio, evidence shows that it covered Franklin County. Glacial till, a mixture of clay, silt, sand, gravel, and boulders deposited directly by the ice, covers much of central Ohio and forms a layer over Battelle - Darby Creek Metro Park. Large boulders called erratics that were not formed in Ohio were carried there by glaciers, and in some places large volumes of meltwater cut deep ravines through the till to the bedrock. More than 25,000 years ago, when animals including the mastodon dominated the landscape, the climate was far colder than today, and during the advance of the last glacier over Ohio, a hot July day would reach only about 60 degrees beneath a mile-high sheet of ice.