'High-Impact' Sports

Thrill seekers are a strain on national park resources not only because of the high cost of rescues but also because of the environmental damage they often wreak. Some of the worst offenders:

MOUNTAIN BIKING: Fat-tired two-wheelers run roughshod over the trails. Weeds and rodents are replacing the rare and delicate plants and animals park visitors go to see.

HIKING: As the number of backpackers mushrooms, the mountain of trash they leave behind inevitably piles up.

ROCK CLIMBING: The chalks used by rock climbers discolor rock faces. And park rangers encounter climbers pulling off vegetation and chipping away at rocks to make for an easier ascent.

SNOWMOBILING: An average of 1,000 snowmobilers cruise Yellowstone Park's packed ice on a given winter day. The whine of snowmobile engines scares off wildlife and may be unpleasant to other park visitors.