The Army set up a tent camp near Mammoth Hot Springs, which eventually evolved into Fort Yellowstone, which the army continued to use until they turned over control of the park (and the fort) to the then newly-formed National Park Service in 1918. The National Park Service used Fort Yellowstone as Yellowstone National Park's headquarters, which has continued to this day.
The Army spent thirty-two years running Yellowstone National Park, the longest period the army ran any national park in United States history.
Fort Yellowstone is also noted by conservationists to have helped define how national parks were to be managed. During its thirty-two years at Yellowstone, the army developed regulations that put much emphasis on conservation. Under the watchful eyes of the army at Fort Yellowstone, the features and wildlife of Yellowstone National Park were protected from vandalism and extinction. In fact, many of the policies initiated by the army at Fort Yellowstone were later adopted by the National Park Service.
In addition, the hats used by the National Park Service rangers (Ranger Stetsons) are descended from the hats originally used in Army uniforms.