Fort Yellowstone, at Mammoth Hot Springs in Yellowstone National Park, was created after the U.S. Army took over protection of the park in 1886 to address poaching, vandalism, and commercial pressure. Established as a permanent post in 1891, it served as the park’s administrative center until 1918, when control passed to the National Park Service. Built in stages from 1891 to 1913, the fort developed into a substantial complex whose surviving buildings now anchor park headquarters. Beyond its architecture, it was a formative center for practices that shaped later national park management, including patrols, wildlife protection, law enforcement, education, and ranger traditions.