The Hayden Geological Survey of 1871 explored the region of northwestern Wyoming that later became Yellowstone National Park in 1872. It was led by geologist Ferdinand Vandeveer Hayden. The 1871 survey was not Hayden's first, but it was the first federally funded geological survey to explore and further document features in the region soon to become Yellowstone National Park, and played a prominent role in convincing the U.S. Congress to pass the legislation creating the park. In 1894, Nathaniel P. Langford, the first park superintendent and a member of the Washburn-Langford-Doane Expedition which explored the park in 1870, wrote this about the Hayden expedition:We trace the creation of the park from the Folsom-Cook expedition of 1869 to the Washburn expedition of 1870, and thence to the Hayden expedition of 1871, Not to one of these expeditions more than to another do we owe the legislation which set apart this "pleasuring-ground for the benefit and enjoyment of the people"

Yellowstone National Park is a national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the 42nd U.S. Congress with the Yellowstone National Park Protection Act and signed into law by President Ulysses S. Grant on March 1, 1872. Yellowstone was the first national park in the U.S. and is also widely held to be the first national park in the world. The park is known for its wildlife and its many geothermal features, especially the Old Faithful geyser, one of its most popular. While it represents many types of biomes, the subalpine forest is the most abundant. It is part of the South Central Rockies forests ecoregion.