Rafters didn't muster the courage to paddle Colorado's Gore Canyon until the 1970s, and it's easy to understand why. This chasm on the Upper Colorado is a six-mile gauntlet of fuming Class IV and V rapids over a half-dozen drops, including a 12-footer. Put in with the national rafting champions at Timberline Tours, which runs full-day trips from August through October. Then hang on for one of the hairiest stretches of whitewater in the country. [$85-$190; timberlinetours.com]