The greatest unsolved mystery of the American Southwest is the fate of the Anasazi, the native peoples who in the eleventh century converged on Chaco Canyon (in today's northwestern New Mexico) and built a flourishing cultural center that attracted pilgrims from far and wide, a vital crossroads of the prehistoric world. The Anasazis' accomplishments--in agriculture, art, commerce, architecture, and engineering--were astounding, as remarkable in their...