Dead Horse Point State Park, UT, near Moab, UT.
It was one of those overcast, dreary mornings when you don't think you're going to get anything decent. I was guiding to photo clients, hoping the sun would break through the clouds behind us for even a minute so my clients could get something decent. Suddenly, the sun popped through a hole in the clouds and I got my clients set up and shooting. After a couple of minutes, I asked them if they minded if I got my camera gear and got a shot, too. They agreed and I ran the 100 yards to my truck, got my gear, ran back, and got the shot as the rainbow was starting to fade. After another minute or so, the hole in clouds closed up and the rainbow and the light on the canyon were gone.
A rain squall passing over the canyon below Dead Horse Point State Park, Utah, produced this vertical rainbow.