"It's well known that Mother River doesn't like a smart aleck," says Patricia McCairen. Accordingly, she plies her oars with reverence and skill on a sometimes hair-raising solo rafting trip along the Colorado River that winds though the stupendous stone valleys of the American Grand Canyon. Like the waters of the Colorado, which change from long, still stretches to boiling white water that barely clothes sharp rocks and hides holes that can suck down a raft, McCairen's moods--and even her name--change as the miles unwind. One moment, she's the cocky, athletic river guide Babe; the next,...