A map drawn based on data collected by Ferdinand Vandeveer Hayden during the Hayden Geological Survey of 1871, showing the area of the then-proposed Yellowstone National Park. The geological survey was the first one funded by the federal government of the United States to explore and further document features in the region, and played a prominent role in convincing the U.S. Congress to pass the legislation withdrawing this region from public auction and creating the country's first national park.Map credit: USGS