Rainbow Falls is the highest waterfall on the Middle Fork of the San Joaquin River, in the eastern Sierra Nevada mountains of California, in the United States. Plunging 101 feet to the turbulent water below, the falls are named for the rainbows that appear in their mist on sunny summer days. Rainbow Falls is located within the boundaries of Devils Postpile National Monument. About 75,000 years ago, lava erupted from a vent just east of the present-day falls.