Great Falls is a chain of five waterfalls along a 10-mile reach of the upper Missouri River in north-central Montana, where the river drops 612 feet and creates one of its most dramatic breaks. Formed by geologic structures in the Great Falls Tectonic Zone and further shaped after the last glacial period, the falls and surrounding landscape preserve major evidence of ancient ice, floodwaters, and river change. Long known to Native peoples, the cataracts entered U.S. exploration history in 1805, when Meriwether Lewis and the Lewis and Clark Expedition encountered them and endured a difficult portage. The falls later became one of Montana’s defining symbols.