Roche-A-Cri is a prominent butte, perhaps the steepest hill in Wisconsin, known to 17th- and 18th-century French voyageurs as La Roche-a-Cri. Rising 300 feet above the surrounding plain, it undoubtedly guided Indians and early pioneers, and Indians of an undetermined cultural group left rock carvings, or petroglyphs, at places on Roche-A-Cri. Like many similar formations on Wisconsin's sandy Central Plain, the butte is composed of Cambrian sandstone about 500,000,000 years old. The flat plain around it is the old bed of Glacial Lake Wisconsin, which covered 1,800 square miles of central Wisconsin some 15,000 years ago, when the buttes stood as islands in the immense lake. Nearby land was purchased for a roadside park in 1937, conveyed to the Wisconsin Conservation Department ten years later, and Roche-A-Cri State Park was established in 1948; it now contains over 400 acres and is listed in the National Register of Historic Places.