Grant signed the legislation setting aside more than 2 million acres of Wyoming, Montana, and Idaho wilderness for public enjoyment, explicitly barring settlement or exploitation of its geysers, canyons, and forests. It established a conservation model — public land held in trust rather than sold or settled — that dozens of nations later copied.
Yellowstone's geysers and hot springs had circulated in American folklore for decades as tall tales too strange to believe — fur trappers spoke of boiling rivers and steam rising from the ground, and most easterners assumed they were exaggerating or drunk. It took organized survey expeditions in 1870 and 1871, including photographer William Henry Jackson and painter Thomas Moran, to produce evidence persuasive enough for Congress.
The bill passed with unusual speed and bipartisan ease, partly because the region was considered useless for farming or ranching, making protection cheap politically. There was no National Park Service yet to manage it — that would not exist until 1916 — so for its first decades Yellowstone was patrolled loosely, at times by the U.S. Army, against poachers and vandals chipping souvenirs off geyser formations.
The park's creation planted an idea that spread worldwide: that a nation could set aside spectacular land purely for its own sake, off-limits to private profit. Within a century, over a hundred countries had established national park systems explicitly modeled on the Yellowstone precedent, from Canada's Banff to South Africa's Kruger.