On March 1, 1872, President Ulysses S. Grant signed legislation setting aside a portion of the federal public domain as "a public park or pleasuring-ground for the benefit and enjoyment of the people." The Yellowstone National Park Protection Act (17 Stat. 32) placed more than two million acres—most of it in the Wyoming Territory, with small portions reaching into Montana and Idaho—under federal reservation. The act required that the park's "natural curiosities" and "wonders" be preserved from injury or spoliation. It said nothing about wildlife.

This omission is not incidental. The founding legislation of the world's first national park was written to protect geothermal features and scenery, not living animals. Yet the park would become, over the following century, one of the central engines of American wildlife conservation—not because its founders intended it, but because the mere act of reserving land from settlement created a refuge that other mechanisms of destruction could not easily reach. The contradiction was present at the creation: a park conceived as a scenic playground became, through necessity and accident, a sanctuary for the last wild bison in the lower forty-eight states, a laboratory for predator eradication, and eventually a site of ecological restoration.

The path to the 1872 act ran through exploration and promotion. Ferdinand V. Hayden, a geologist with the U.S. Geological Survey of the Territories, led an expedition through the Yellowstone region in 1871. His report to Congress—UNVERIFIED in exact detail pending primary-source confirmation—apparently helped build legislative support, though the precise role of his findings versus the political maneuvering of railroad interests and territorial boosters remains a subject of scholarly attention. Nathaniel P. Langford, who became Yellowstone's first superintendent in 1872, was also a promoter of the Northern Pacific Railway, though the details of his dual role require further primary-source documentation. The park was, from its inception, entangled with both scientific curiosity and commercial ambition.