see more

YELLOWSTONE, MT - FEBRUARY 17: A trio of snowmobilers enter Yellowstone National Park February 17, 2003 in west Yellowstone, Montana. Traditionally, Presidents' Day three-day weekend is the busiest winter weekend at Yellowstone National Park. The National Park Service plans to release part of a study called 'Final Supplemental Environmental Impact' February 21, 2003 to demonstrate that the Bush administration's proposal is not the best alternative for the environment, concerning the proposed snowmobile ban in Yellowstone and Grand Teton national parks. Environmentalists called for a ban on the snowmobiles due to the noise and smog they produce. (Photo by Bill Schaefer/Getty Images)

YELLOWSTONE, MT - FEBRUARY 17:  A trio of snowmobilers enter Yellowstone National Park February 17, 2003 in west Yellowstone, Montana. Traditionally, Presidents' Day three-day weekend is the busiest winter weekend at Yellowstone National Park. The National Park Service plans to release part of a study called 'Final Supplemental Environmental Impact' February 21, 2003  to demonstrate that the Bush administration's proposal is not the best alternative for the environment, concerning the proposed snowmobile ban in Yellowstone and Grand Teton national parks.   Environmentalists called for a ban on the snowmobiles due to the noise and smog they produce.  (Photo by Bill Schaefer/Getty Images)