Thousands of years ago, glaciers covered northern and central Ohio. As the glaciers retreated, melting ice created rivers and streams that carved valleys and exposed land surfaces. Glacial till in the form of clay, gravel, sand, silt, and boulders was directly deposited by the ice and covered most of the central Ohio countryside. Evidence of this material can be seen along stream beds and nature trails. The Darby Creeks continue to deepen their valleys today, as moving water continues what the glacier began.