President Grant signs the bill creating the nation’s first national park at Yellowstone.

Native Americans had lived and hunted in the region that would become Yellowstone for hundreds of years before the first Anglo explorers arrived. Abundant game and mountain streams teaming with fish attracted the Indians to the region, though the awe-inspiring geysers, canyons, and gurgling mud pots also fascinated them.

John Colter, the famous mountain man, was the first Anglo to travel through the area. After journeying with Lewis and Clark to the Pacific, Colter joined a party of fur trappers to explore the wilderness. In 1807, he explored part of the Yellowstone plateau and returned with fantastic stories of steaming geysers and bubbling cauldrons. Some doubters accused the mountain man of telling tall tales and jokingly dubbed the area “Colter’s Hell.”

Before the Civil War, only a handful of trappers and hunters ventured into the area, and it remained largely a mystery. In 1869, the Folsom-Cook expedition made the first formal exploration, followed a year later by a much more thorough reconnaissance by the Washburn-Langford-Doane expedition. The key to Yellowstone’s future as a national park, though, was the 1871 exploration under the direction of the government geologist Ferdinand Hayden. Hayden brought along William Jackson, a pioneering photographer, and Thomas Moran, a brilliant landscape artist, to make a visual record of the expedition. Their images provided the first visual proof of Yellowstone’s wonders and caught the attention of the U.S. Congress.

Early in 1872, Congress moved to set aside 1,221,773 acres of public land straddling the future states of Wyoming, Montana, and Idaho as America’s first national park. President Grant signed the bill into law on this day in 1872. The Yellowstone Act of 1872 designated the region as a public “pleasuring-ground,” which would be preserved “from injury or spoilation, of all timber, mineral deposits, natural curiosities, or wonders within.”

For a nation bent on settling and exploiting the West, the creation of Yellowstone was surprising. Many congressmen gave it their support simply because they believed the rugged and isolated region was of little economic value. Yet the Yellowstone Act of 1872 set a precedent and popularized the idea of preserving sections of the public domain for use as public parks. Congress went on to designate dozens of other national parks, and the idea spread to other nations around the world.

READ MORE: The National Park Service