The Mammoth Hot Springs Historic District is significant as the administrative and concession headquarters of the largest national park in Wyoming. It is important for its historical association with the development of Yellowstone National Park and with the development of administrative and concession policies in Yellowstone and the national park system. The district's location, near one of the major natural curiosities in the park, the Mammoth Hot Springs Terraces, and at the juncture of the first entrance road to the park resulted in its selection as the site of the first administrative headquarters and the site of the first concessions in the first national park in the United States. The first hotels in Yellowstone were located at Mammoth Hot Springs, as well as the first retail store, photograph shop, and filling station, the successors of which still operate within the district. The army era in the national parks is also associated with the district, which includes Fort Yellowstone, the best-preserved post representing the early military efforts to protect the nation's natural resources. The district is also important for its association with the early history of the National Park Service, reflecting the influence of that agency on park development in areas such as preserving natural features and scenic resources, responding to the popularity of the automobile, creating museums and educational programs, and incorporating master plans in park design. The district is also associated with the history of New Deal era public works programs, having benefited from several projects which provided funding and manpower for improvements and new construction.
Mammoth Hot Springs is also significant for its architecture. Fort Yellowstone, within the district, reflects the layout and architecture of a typical western army fort of the late nineteenth century, and is remarkable for its level of integrity, the masonry displayed in its native sandstone buildings, and the substantial quality of its construction. The buildings of the military period are representative of the work of the United States Quartermaster Corps, Hiram Chittenden, and Reed and Stem. Buildings erected after the military era in the administrative area of the district are significant for their representation of the work of architects of the National Park Service, and the landscape of the district reflects the influence of the agency's master plans and the efforts of its landscape architects. Government buildings of the post-military era include fine representatives of French Renaissance and English Tudor style architecture. The concession area buildings are notable for their reflection of the evolution of park commercial architecture from the late nineteenth through the mid-twentieth centuries. Included within the district are concession buildings which are excellent representatives of Colonial Revival, Rustic, Prairie, and Art Moderne styles. The work of architects hired by concessioners, including Robert C. Reamer, Fred Wilson, and Douglas McLellan, is also represented in the district.