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Yellowstone National Park
Yellowstone National Park, the world's first national park, was set aside in 1872. That year, 300 hardy souls visited the park. In 1883, the number of visitors jumped to 5,000 per year with the addition of a stop on the Northern Pacific Railroad. More than 3 million people per year visit the park today.
Yellowstone's famous geyser, Old Faithful, pictured above, is a cone geyser in Wyoming that can shoot up to 8,400 gallons (32,000 liters) of piping hot water up to 185 feet (56 meters) into the air. The water works can last up to 5 minutes long. Eruptions are currently about 90 minutes apart.