Fur trappers' fantastic tales of cauldrons of bubbling mud and roaring geysers sending steaming plumes skyward made their way back east. Several expeditions were sent to investigate, opening the West to further exploration and exploitation. In 1871, Ferdinand Hayden led an expedition that included artist Thomas Moran and photographer William H. Jackson. They brought back images that helped convince Congress that the area known as Yellowstone needed to be protected and preserved.

In 1872, President Ulysses S. Grant signed a law declaring that Yellowstone would forever be "dedicated and set apart as a public park or pleasuring ground for the benefit and enjoyment of the people."