The Great Falls of the Missouri - The Great Falls of the Missouri might have looked like this when encountered by the Corps of Discovery (A). The falls are actually five separate falls, the largest of which is called the Great Falls. Each of these falls are created by a resistant sandstone unit in the Cretaceous Kootenai Formation. A dam and hydroelectric generation plant are currently located on the site (B). (Lewis and Clark, 6/13-7/14/1805)