About 70,000 years ago, after a brief, warm interglaciation following the Illinoian glaciation, ice once again began to build in northern Canada and slowly advance southward. This was the beginning of the last major glaciation in Ohio. By about 24,000 years ago, the Wisconsinan glacier reached Ohio and by about 18,000 years ago, the ice had reached its maximum southward extent, covering nearly two-thirds of the state. As the climate once again warmed, the Wisconsinan glacier began to melt and retreated northward, finally leaving Ohio about 14,000 years ago. Much of the landscape in the glaciated portion of Ohio is the result of the Wisconsinan glacier. Thick deposits of till, deposited as ground moraine, sand and gravel outwash from the melting glacier along larger stream courses, lobate ridges or hills of till are recessional moraines, marking a pause of the retreating ice, and other features prominent in Ohio record the presence of this massive ice sheet only a few thousand years ago.