In the winter of 1804-1805, the Lewis and Clark Expedition set up camp in the Mandan Villages. A replica of that site has been established at the Fort Mandan Visitor Center in Washburn, ND.
You can actually learn a little of the Mandan language on the website managed by the Mandan, Hidatsa and Arikara Nations! The title-line for this blog entry links to a sample lesson. This language is rapidly disappearing, as the Mandan Nation was decimated by smallpox after exposure to early European explorers.
The Three Affiliated Tribes (specified above) are located in the Fort Berthold Indian Reservation in North Dakota. The McLean National Wildlife Refuge, managed by the Audubon National Wildlife Refuge, is located within the reservation's boundaries.