This image was captured in Yosemite Valley, about three hours east of San Francisco, California.
The history of this shot goes back many years. I was in Yosemite to shoot a "moonbow" reflection shot like this when I captured my image that ended up on the cover of the October 2011 issue of Outdoor Photographer. A storm rolled in on that night, so the moonbows that would have been available were not present yet.
Astronomical events always motivate me to get out shooting at night. Every spring around the time of the full moon, the moonlight creates rainbows in the spray of Yosemite's waterfalls. These "moonbows" form at predictable times as the geometry works out just right to refract the sun's light bounced off the moon and into and back out of the tiny drops of water. Two reflections within a water drop form the main rainbow, and if a second one forms, it's after a third reflection, so the order of the colors is reversed.