Originally the post exchange, this building served as a recreation hall for the stationed men. The exchange evolved from the post trader’s store, an integral element in early forts where the men could buy staples and supplies. As early as 1888, the post exchange or canteen had replaced the post trader’s store. In time, the post headquarters began to carry food, clothing, jewelry, personal effects, gifts, and other items so that personnel could shop for almost any occasion without leaving the post. Built in 1906 for $21,800, the building served as the post exchange until 1962 when it became the post headquarters. Under the army’s sell/lease program, the Naval Reserve training center was located here. The building has since housed Forest Service personnel, the U.S. Army facilities manager, and the Montana Natural History Center.