Here in the Great Sand Dunes of Colorado, eolian sand from the upper Rio Grande, in the San Luis Valley, has accumulated against the Sangre de Cristos and formed massive dunes amidst the prevailing southwesterlies. However, on this afternoon in 2003, northeast outflow winds from earlier mountain thunderstorms blew cold outflow the opposite way, tossing sand off the dune crests. The low angle of sunlight, and its partial diffusion by clouds to soften dynamic range a bit, made a wonderfully textured scene, looking across the top of this dune toward the shadowed side of the next.
