A common reaction to this picture is, "You sure were lucky that cloud came floating by."
Actually, it was just lingering in the sky, waiting for someone to notice it.
As I rounded the corner on the Kolob road in a quest for good sunset scenes, the cloud and Taylor Creek and the deepening red of a lowering sun all cried out, "Hey, grab it while you can!"
A 4x5 is hardly a snapshot camera but I had it ready very quickly, anxious that clouds to the west might eclipse the lighting before I was set up.
The lens was a 65mm Super Angulon affording a very wide angle of view. Ultra-Wide angle lenses on view cameras have a curious effect on exposure because they are so close to the film plane at the center but relatively far from the film at the edges. The center gets maybe two to four times as much light as the corners.
A radially graduated filter placed over the front of the lens can even out the exposure, but in this case I was seeking the dark edge effect. Using a spot meter I set the exposure to optimize for the midway circle, allowing the center to be slightly over exposed, the edges to be under exposed, and the cloud to be perfectly exposed.
Nowadays I could use a graduated radial mask in Photoshop to even out the exposure. Nah. Leave it as Nature and Optics created it.