Photograph by Wikimedia Commons user Djngsf of mushroom shaped rock formations near a hiking trail at Garden of the Gods in Shawnee National Forest, Illinois.
Photograph of the Giant City Stone Fort Site, Stone Fort Road, Makanda, Illinois, by Wikimedia Commons user Dazspell in 2013. The fort is a pre-Columbian Late Woodland (600-900 C.E.) stone enclosure.