They appear gradually as you approach. First, an amorphous khaki blob hugging the base of the Sangre de Cristos. Then, a tan curtain that has fallen off the rod and rumpled onto the floor. And then, about four miles south of them, they come into focus: massive, improbable, creamy peaks of sand slapped against 14,000-foot peaks.
These are the Great Sand Dunes, and photographing their ever-changing forms at sundown is an intoxicating experience.