The Chase Rock: A Glacial Erratic

Sitting in a suburban Chicago yard, this boulder does not belong here. Geologists call it a glacial erratic, a rock carried far from its place of origin by a moving glacier and dropped when the ice finally melted. This particular granite almost certainly originated in Canada.

During the Pleistocene Epoch, which began about two and a half million years ago, massive ice sheets advanced southward across the continent. When the last glacier retreated about ten thousand years ago, it left behind boulders like this one scattered across the Illinois landscape, geologic calling cards from an era when Chicago sat under a mile of ice. Excavated on this property in nineteen ninety-eight, the Chase Rock is a quiet reminder that the ground beneath the suburbs has its own deep history.