Yellowstone National Park

1. The Grand Prismatic Spring, the largest in the United States and third largest in the world, and it's colored bacteria and microbial mats in Yellowstone National Park, Wyoming, June 22, 2011. REUTERS/Jim Urquhart

2. Hayden Valley and Yellowstone River. Photo by John Brandow

3. A coyote walks in Yellowstone National Park, Wyoming August 11, 2011. REUTERS/Lucy Nicholson

4. A chipmunk sits on a rock in Yellowstone National Park, Wyoming August 13, 2011. Picture taken August 13, 2011. REUTERS/Lucy Nicholson

5. Yellowstone River and Washburn Range in Hayden Valley. Photo by J Schmidt

6. Old Faithful Geyser, the first geyser in the park to be named erupts in Yellowstone National Park, Wyoming, June 22, 2011. Currently the geyser erupts approximately every 90 minutes. REUTERS/Jim Urquhart

7. A grizzly bear walks in a meadow in Yellowstone National Park, Wyoming in this August 12, 2011 file photo. Each one of the 2,000 bear-proof trash cans at every picnic table, trailhead and vault toilet in Yellowstone must be emptied every day to prevent food waste and other smelly garbage from attracting grizzly bears. 429 seasonal employees of the National Park Service join more than 3,200 workers hired by private concession operators each summer to perform a variety of unheralded, behind-the-scenes duties that keep Yellowstone running smoothly, even during the busiest days of summer. REUTERS/Lucy Nicholson/Files.

8. A hiker drinks from a water bottle in front of Heart Lake in the Red Mountains of Yellowstone National Park, Wyoming August 10, 2011. REUTERS/Lucy Nicholson

9. Yellowstone's Electric Peak. Photo by J Schmidt

10. An aerial view of Excelsior Geyser Crater and Grand Prismatic Spring. Photo by Jim Peaco

11. The Yellowstone River Lower Falls is seen at sunrise in Yellowstone National Park, Wyoming August 11, 2011. Picture taken August 11, 2011. REUTERS/Lucy Nicholson

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