I was hiking in the Superstition Mountains, AZ as a storm was moving into the area. I came around a bend in the trail and this image of a storm cloud over the Goldfield Mountains presented itself. The rains moved in 5 minutes after this was taken.
Camera - Canon 5D MkIII
Lens - Canon 24-105
Exposure - 1/800 @ f11
Focal length - 58mm
ISO - 800