Baja California, MéxicoKicking up a cloud of dust, the caravan of pack burros and mules lurches toward the gate of the corral, trailed by a lean cowboy in a crisp white shirt whose spurs jangle in rhythm with his horse’s gait. At least three times a week, 34-year-old Eleonary “Nary” Arce Aguilar must drive down from his drought-stricken ranch to load up on critical water supplies that allow his family to stay on their ancestral land on the high mesa of Baja, México’s Sierra de San Francisco.

As the animals gulp from the trough, Nary takes a long drink from a PVC pipe that connects to a mountain spring eight miles away—a lifeline for the handful of ranches that survive in this remote