Four days ago I sat in eight or so feet of crusted snow atop Loveland Pass—two miles, plus 1,402 feet above where I am now. From up there I surveyed the first verdant reach of Colorado River drainage, the valley of the Snake River. And, probably because of oxygen deprivation, I determined I should see the rest—all 1,450 miles—of that drainage. So I pushed my truck into neutral (1,450 miles is a long way), let off the brake, and rolled on down the western face of the Divide.