The Modoc Rock Shelter site was discovered in 1951 by archaeologist Irvin Peithmann after road grading exposed artifacts on the surface under or near the bluff along Bluff Road. His observation led to major excavations in the 1950's and 1980's, mostly by the Illinois State Museum. The artifacts showed that the rock shelter served as a short-term camp 9,000 years ago, a long-term camp by 6,000 years ago, and again as a hunting camp 4,000 years ago. Evidence from the site shows that its inhabitants ate deer, raccoon, opossum, birds, and fish. The bluffs had provided shelter for more than 9,000 years, and the deposits there were the first stratified archaic deposits found in Eastern North America.