Just south of where the Illinoian glacier stopped lie massive escarpments—the backbone of southern Illinois. The landscape is characterized by high, east-west sandstone cliffs that form the Greater Shawnee Hills. Lower hills underlain by limestone and sandstone are known as the Lesser Shawnee Hills. The topography is very rugged, with many bluffs and ravines. Clear, rocky streams widened and deepened the ravines forming canyons, shelves, steps, and shelter bluffs. Where the slopes are steep, bare rock is exposed. Most of this division was forested, yet openings occurred—barrens and glades. Barrens are grassy openings found on rocky, south- facing slopes that have only a thin layer of soil. Vegetation includes small, gnarled, and twisted blackjack and post oaks. Prairie grasses and the occasional blazing star grow here. Glades are open expanses of bedrock on bluff tops, dominated by red cedar. Although prairie grasses such as little bluestem occur, the ground is likely to be covered with moss and lichens. This division is divided into two sections, the Greater Shawnee Hills, of which Ferne Clyffe State Park is a good example, and the Lesser Shawnee Hills. Cave in Rock State Park is found in this section.