Old Faithful and the majority of the world’s geysers are preserved in Yellowstone National Park. They are the main reason the park was established in 1872 as America’s first national park—an idea that spread worldwide. A mountain wildland, home to grizzly bears, wolves, bald eagles, cutthroat trout, and herds of bison and elk, the park is the core of one of the last, nearly intact, natural ecosystems in the Earth’s temperate zone.