The west wind blows unhindered across the San Luis valley of Colorado's southeastern corner, until it meets the Sangre de Cristo mountains. There it rises and drops its burden of fine sand, over the eons forming sand dunes. Storm winds from the east, flowing through and over the Mosca, Medano, and Music mountain passes, piles the sand back onto itself, forming the highest dunes of North America. In this photograph you see the four wheel road over Mendano Pass and a view the wilderness where east wind meets dunes, forming those sand ramps in the distance. The atmospheric effects are provided by an approaching summer thunderstorm. I was a bit anxious, standing there with my aluminum lightning rod (otherwise used as a tripod) because the storm was literally behind me.