Fort Yellowstone was a U.S. Army fort, established in 1891 at Mammoth Hot Springs in Yellowstone National Park. Yellowstone was designated in 1872 but the Interior Department was unable to effectively manage the park. Administration was transferred to the War Department in August 1886 and General Philip Sheridan sent a company of cavalry to Mammoth Hot Springs to build a cavalry post. The army originally called the post Camp Sheridan in honor of General Sheridan but the name was changed to Fort Yellowstone in 1891 when construction of the permanent fort commenced. The army administered the park until 1918 when it was transferred to the newly created National Park Service. The facilities of Fort Yellowstone now comprise the Yellowstone National Park headquarters, the Horace Albright Visitor Center and staff accommodations.

Mammoth Hot Springs is a large complex of hot springs on a hill of travertine in Yellowstone National Park adjacent to Fort Yellowstone and the Mammoth Hot Springs Historic District. It was created over thousands of years as hot water from the spring cooled and deposited calcium carbonate. Because of the huge amount of geothermal vents, travertine flourishes. Although these springs lie outside the caldera boundary, their energy has been attributed to the same magmatic system that fuels other Yellowstone geothermal areas.