Fort Abraham Lincoln State Park in North Dakota preserves two distinct histories at the meeting of the Heart and Missouri rivers: the Mandan village of On-a-Slant and a later U.S. Army post. Established around 1575, On-a-Slant was a fortified Mandan community of earth lodges that prospered through farming, bison hunting, pottery, and trade until a smallpox epidemic in 1781 forced survivors to move north. In 1872 the Army built Fort McKeen here, soon renamed Fort Abraham Lincoln, which became associated with George A. Custer, the 7th Cavalry, and their departure for the Great Sioux War of 1876. Abandoned in 1891, the site later became a state park with extensive reconstructions reflecting both Indigenous and military history.