Rainbow Falls is a very popular hike in Devils Postpile National Monument, and with good reason. It is a moderate downhill grade to the falls, the upper falls are surprisingly impressive, and the lower falls are small but beautiful with a great swimming hole beneath the falls.
From the parking area just before the Red’s Meadow Lodge (stop #9 on the shuttle), the trail heads mostly downhill through some nice pine/fir forest and some areas that were badly burned in a fire in 1992. The trail crosses the John Muir Trail and Pacific Crest Trail shortly after the trailhead. It is just over a mile to the overlook at the top of the upper falls. The falls are on the middle fork of the San Joaquin River. The falls cascade about 100 feet, and when they are at full flow in summer they display a nice rainbow at midday.
The trail that once wound down to the base of the falls has been closed for a few years, but the main trail continues down for another half mile to the much smaller lower falls. This little cascade flows through granite boulders and falls into a large pool with a beach that is very popular for swimming in hot weather.