MY HIKE BEGAN AT DAWN on the South Rim of the Grand Canyon. By 9 a.m. I stood waiting on the beach at Phantom Ranch for the dozen other members of the crew to arrive with five rafts, three kayaks, two inflatable pack rafts, and nearly 5,000 pounds of gear, food, and beverages. They launched a week before, at Lees Ferry, 90 miles upstream. The measurable depth of the canyon, more than a vertical mile, can’t compare to the trench the Colorado River has carved in the human imagination.