ON THE TRAIL, Grand Canyon National Park. A muleback party leaving the South Rim on the long and exciting descent over the Bright Angel Trail into the depths of the Canyon. Down in the gorge, hidden by many plateaus and smaller gorges, is the Colorado River which during the ages cut down through layers of rocks millions of years in the making and reached some of the oldest rocks known to geologists. It is still cutting, and on the average carries nearly half a million tons of suspended silt past any given point each 24 hours. A suspension bridge across the river leads to Phantom Ranch, the overnight stop on two-day trail trips. (Courtesy, Josef Muench Pictorial Photography.)