Approaching Great Sand Dunes from U.S. Highway 150. These dunes were formed and are maintained by winds that blow sand across the arid San Luis Valley to the western face of the Sangre de Cristo Mountains (seen behind the dunes in this picture). The 14,000-feet-high Sangre de Cristo Mountains are an effective trap for the sand. We pulled in during an unusual rainy spell, so my pictures have a different "flavor" than you would normally see for this place. For scale, the height of the dunes is about 700 feet, and they run for several miles.

Colorado hospitality: "Welcome to Great Sand Dunes folks!"

To walk on the dunes, you must cross Medano Creek. The relaxing gurgle of the cool Medano Creek water and the view of the wavy dunes lit by the evening sun escaping through heavy clouds made for a surreal experience.

Hiking on the dunes. Distances were deceiving. We walked for about a half mile across a flat plain of sand just to get to the dunes. This was a cloudy morning, which didn't make for good photography. However, the clouds provided welcome relief from what would have been 90-100 degree weather. We didn't complain!

Hiking up the steep dunes. There are no established trails because the sand shifts on a daily basis. It took about an hour and a half to get to the top of the highest dune.

Waves of sand

A giant sand box! What a fascinating place!