Glaciers and Prairie

Continental glaciers of the Great Ice Age scoured and scraped the land surface, pushing up chunks of bedrock and grinding them against each other and along the ground as rock-laden ice sheets moved southward. The rock here is a glacial erratic, carried and shaped in ice flowing south from northern Wisconsin or Michigan and deposited at the end of the last ice age about 15,000 years ago. Its gouged grooves, parallel striations, and polished surfaces formed as the boulder ground against other rock formations and sand grains in moving glacial ice. By the early 1800s, a tall grass prairie covered much of the area, with glacial deposits forming the parent soils that were enriched over thousands of years by thick prairie vegetation. These fertile prairie soils proved ideal for farming, and much of the prairie in Illinois has since been converted to farmland. Native prairie plants still grow around the boulder, and Big Blue Stem grass sometimes grew tall enough to hide a person on horseback.

Summit, Illinois · United States