Tourists watch the 'Old Faithful' geyser

Tourists watch the 'Old Faithful' geyser which erupts on average every 90 minutes in the Yellowstone National Park, Wyoming on June 1, 2011. Yellowstone National Park, was established by the U.S. Congress and signed into law by President Grant on March 1, 1872. The park is located primarily in the U.S. state of Wyoming, though it also extends into Montana and Idaho and was the first national park in the world. It is known for its wildlife and its many geothermal features, especially the Old Faithful Geyser. AFP PHOTO/Mark RALSTON (Photo credit should read MARK RALSTON/AFP via Getty Images)