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Established in 1872, Yellowstone National Park is a national treasure. Located primarily in Wyoming, the park also extends into Montana and Idaho. Yellowstone has active geothermal features with geysers and boiling mud pots throughout the park. The most famous is Old Faithful, a geyser that has erupted on the clock for decades. Travelers be warned, July is the busiest month of the year, with almost a million visitors alone. The park has a tour bus system, nine visitor centers, and 2,000 campsites.