Beginning in the high country of Yosemite National Park, the Merced River makes a headlong rush through glacially-carved canyons, rugged mountains and foothills to the San Joaquin Valley. Ample access points allow you to float rapids at your own pace. Come ashore long enough to watch an eagle dive for its dinner. Hook a trout and plunk it in a pan over an open fire at Railroad Flat or McCabe Flat campgrounds.