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There is an origin story about Yellowstone National Park that involves weary explorers sitting around a campfire, extolling the beauty of the land they’ve just seen and vowing to ensure it becomes a public park for all to enjoy. It’s a vision of altruism and environmentalism that suits the founding of the world’s first national park—only it’s not entirely true.
The members of the 1870 Washburn-Doane Expedition did likely gather for campfires as they explored the region’s geysers and rivers and waterfalls, and they did likely discuss the best use of the land they were exploring. But, as with so much of American history, there were significant corporate interests at play. Yellowstone might never have become the public parkland it is today if not for the Northern Pacific Railroad Company.
Before the explorers set out on their expedition, Northern Pacific was strategizing to expand across the Montana Territory. An influx of tourism in the region would be a boon to business, so a railroad financier, Jay Cooke, began lobbying for an expedition. To drum up excitement back east, one member of the expedition, a politician named Nathanial P. Langford, toured the country giving lectures about the beauty of Yellowstone. Meanwhile, Northern Pacific subsidized an artist to sketch images of the park for display in Washington, D.C.
In March of 1872, less than two years after the expedition, Congress enacted the Yellowstone Park Act, ensuring that the land would remain under the purview of the Department of the Interior rather than being divvied up among private individuals—an arrangement that would attract visitors to the area, which would be sure to benefit big business like the railroad company.
Seventy years into the park’s existence, LIFE dispatched Alfred Eisenstaedt to photograph its geographic features, during a summer that was shaping up to be its biggest yet for tourism. In that record year, 1946, the park saw more than 800,000 visitors. In 2014, it saw 3.5 million. Though the idea might seem incongruous, all 167 million visitors who have encountered its bison and watched Old Faithful blow (since recordkeeping began in 1904) have corporate interests to thank for one of America’s greatest natural wonders.
Liz Ronk, who edited this gallery, is the Photo Editor for LIFE.com. Follow her on Twitter @lizabethronk.