Millstone Bluff, a natural bluff in southern Illinois near Glendale in Pope County, preserves an important prehistoric Native American site associated with Mississippian cultures. On its summit are traces of a village, a prehistoric stone box cemetery, a rock art site, and a Late Woodland stone fort, showing the bluff’s significance across more than one cultural period. Its most notable surviving features are petroglyphs depicting two thunderbirds, pipes, axes, a spider-like figure, turkey tracks, a humanoid form, and a cross-and-circle design seen at other southern Illinois sites. It is protected within Shawnee National Forest and recognized for its archaeological importance.