Stand at the rim of Palo Duro Canyon or look down from any vista along the caprock, and let your imagination take over. Beneath an endless canopy of blue, you find yourself at the edge of an enormous island of rippling grassland that stretches from the New Mexico borderlands down through the Texas Panhandle. The Llano Estacado, Coronado's legendary "staked plains," comprises all or part of thirty-three counties in Texas and four in New Mexico. It...