Book excerpt: From perpetually snow-capped peaks to stifling deserts below sea-level, the Colorado cuts the deepest and truest cross-section through the heart of the continent.It flows through time as well as space. At the bottom of the Grand Canyon lies one of the early layers of the earth's crust. The cliff dwellers' civilization, and the rise and fall of the great pueblos were only a brief moment in its history. Later came the Spaniards, and then the trappers and prospectors. Not so long ago the Indians battled to defend their invaded country and new technological developments--the greatest is which is Boulder Dam--are beginning to change the face of a region other generations were unable to alter. Frank Waters, a native to Colorado, has brought to his book an understanding of the relation between man and nature which is part of his Indian heritage.