For three million years, Colorado's San Luis Valley was filled with water: "Lake Alamosa." Then about 440,000 years ago, the water overran a volcanically created "dam," cutting a deep gorge as it flowed south and joined the Rio Grande. Today, the Valley is the world's largest alpine valley. But Lake Alamosa remains in the form of an underground aquifer that, along with the Rio Grande, nourishes this unique region. This water of life creates a place...