The remarkable Sierra San Luis forms the nexus of the Sierra Madres and the Rocky Mountains. The range runs north-south in the shape of a sleeping lizard. The high narrow pyramid of a head, Animas Peak, rests in the bootheel of New Mexico, and with a thin neck draped across the border the slumbering body curls into the Mexican states of Chihuahua and Sonora. Along the spine is a high ridge covered with sparse patches of six kinds of pine trees. The...