When Yellowstone National Park was created little was known about the area and there were few if any competing interests. Congress just slapped down a generous square centered on the famous geothermal areas, no matter that it didn't match up with state boundaries. So although the park is almost entirely in Wyoming, its north and west entrances are in Montana.The triumphal arch was built in 1903, the cornerstone laid by President Theodore Roosevelt. In the early days this was the main park entry because a railroad came up the river to Gardiner. The inscription reads "For the Benefit and Enjoyment of the People".