'glacial escarpment runs through there' - meaning the glacier stopped before getting to the park?
That's what happened to the southern Il. spot I referred to above. When you get to that moraine in southern, it marks the most southern spot attained of the 4 glaciers that invaded the state. Southern Illinois is actually part of the Shawnee National Forest and remains of the Ozark Mountains make up the un-Illinois type landscape. A state park called Giant City there reminds me of your park.
