Glacial erratics Northeastern Illinois was once a vast glacial plain, similar to the landscapes of the Antarctic today. In the cold, ice and bedrock, there was very little life. photo by Phil Cihlar Wolf Road Prairie is located on the Tinley Ground Moraine which was formed as the glacier retreated -- over 14,000 years ago. As the climate warmed and the ice sheet melted, huge boulders trapped in the ice, similar to this one, came to rest on the ground. photo by Sue Van Horn