The red-roofed, multi-chimneyed buildings found in Mammoth Hot Springs once housed the U.S. Calvary. Why did Yellowstone need an army post? The park's small staff was no match for the poachers, souvenirs hunters and developers that sought to exploit America's first national park in its early years. To protect Yellowstone, the Secretary of the Interior turned to the Secretary of War. Fort Yellowstone was established in 1886 and Yellowstone National Park was protected by the Calvary for the next 30 years to 1916. And while the buildings erected by the Calvary no longer house officers and enliste... Read Mored men they serve as park headquarters, visitor center and museum.