On a crisp day this fall I drove southeast from Grand Junction, Colorado, into the Uncompahgre Valley, a rich basin of row crops and hayfields. A snow line hung like a bowl cut around the upper cliffs of the Grand Mesa, while in the valley some farmers were taking their last deliveries of water, sowing winter wheat and onions. I turned south at the farm town of Delta onto Route 348, a shoulder-less two-lane road lined with irrigation ditches and dent corn still hanging crisp on their browned stalks. The road crossed the Uncompahgre River, and it was thin, nearly dry.