Rainbow Falls drops 101 feet into a red-volcanic-rock canyon on the Middle Fork of the San Joaquin River, making it one of the largest waterfalls in the Sierra Nevada. The red cliff walls, fed by springs and glacial melt from above, create a permanent mist at the base that refracts sunlight into a rainbow when conditions are right — which is most clear summer mornings.
The trailhead is accessed by shuttle from the Mammoth Mountain Inn during peak summer season, and the hike from the shuttle stop to the falls is around two miles each way on a well-maintained trail. It can also be combined with a visit to Devil's Postpile National Monument, which lies along the same trail corridor. The canyon walls make the falls feel enclosed and dramatic rather than simply tall, and the viewpoints — at the rim and at the base, reached by a steep side trail — offer very different perspectives.