At its maximum about 20,000 years ago, the Wisconsinan glaciers covered much of northern Illinois.

When the glaciers finally melted 10,000 years ago due to warmer and drier climate, the surrounding vegetation of tundra and conifers retreated as well, replaced by grasses and forbs such as Prairie Smoke (Geum triflorum) .

The new landscape supported grazers such as mammoths and large predators such as saber-toothed cat, as well as migrants from Asia.