1,000-MILE SUMMER-V631At three o'clock one sleepless night, Colin Fletcher decided that what he must do was walk the length of California. He could only fumble with the supporting reasons, but he knew it was a hike he had to make. Fletcher followed lonely stretches of the Colorado, crossed the Mojave, walked the trough of Death Valley and wandered through the High Sierras. Along the way he stumbled across an unspoiled ghost town and visited frontiers unseen by most