July, August, and September are the "monsoon" months in the southwestern deserts of the United States. Days often start out clear and sunny, but as the heat builds during the day, so do the clouds. Eventually there may be rain, light or heavy, in the afternoon and evening. Because the storms are transient in nature, cloud breaks occasionally allow sunlight to illuminate the passing rain and create dramatic rainbows. At sunset, these high-arching rainbows are particularly rich in the warmer colors of the spectrum, mirroring the warm light that is a hallmark at this time of day.

This image was taken from a roadside pullout about 10 miles north of Kayenta, Arizona just before sunset. The glowing peak at the left end of the rainbow is known as "Agathla Peak" on topo maps and locally as "El Capitan" or "El Cap." According to the topo map, it rises over 400 feet above the surrounding land. Geologically, it is a lava plug, the erosional remnants of the throat of a volcano that solidified around 27 million years ago.