This rare type of rainbow is called a circumhorizontal arc, and it was photographed on June 3 in northern Idaho near the Washington State border. The arc spanned several hundred square miles of sky and lasted for about an hour.
“It is caused by light passing through wispy, high-altitude cirrus clouds. The sight occurs only when the sun is very high in the sky (more than 58° above the horizon). What's more, the hexagonal ice crystals that make up cirrus clouds must be shaped like thick plates with their faces parallel to the ground.” – National Geographic