Then this unusual formation caught my eye—several broad streaks radiating from an area to the east, behind the hogback, like faint streams of sediment in an otherwise clear stream. The only explanation I can offer is contrails, spread laterally by winds aloft, or what, according to Wikipedia, would be called decaying contrails. This is suggested by comparison with the relatively coherent trail to the right.
A sky without contrails, or artificial clouds, would have been standard not so very long ago. Here's a better view of the hogback, one of my all-time-favorite geographic features, showing the west, or scarp, face of the Dakota Group sandstones that create the ridge.
Posted for Skywatch Friday, where many more skies await you.