It is understandable if one is surprised, even a bit mystified, by the presence of massive sand dunes in the mountainous state of Colorado. But exist they do, on the western flanks of the Sangre de Cristo Mountains. And massive they are, rising some 750 feet from the floor of the San Luis Valley and covering many thousands of acres. From close up, it is difficult to get a sense of their scale. Even from the distant vantage point of this photo, I had to stitch together five images to capture the broad sweep of the dunes and the mountains for scale and context. And because of the extreme contrast, I had to make three different exposures at each angle (which I combined using HDR software), making a total of fifteen shots that went into making this panorama. One of my challenges was to make those exposures quickly, to minimize the effects of the moving clouds, which required careful planning of the angles and a practice run, before making the final exposures.