The formation of Devils Postpile began when basalt lava erupted in the valley of the Middle Fork of the San Joaquin River. As lava flowed from the vent, it filled the valley near the Postpile to a depth of 400 feet. Recent radiometric dating of rocks thought to correlate with basalt of Devils Postpile suggest an age of less than 100,000 years.
Approximately 10,000 years ago, glaciers flowed down the Middle Fork of the San Joaquin River. This moving ice easily overrode the fractured mass of lava and quarried away one side of the Postpile, exposing a sheer wall of columns 60 feet high.
Many fallen columns now lie fragmented on the talus slope below. A hike to the top of the Postpile reveals not only a cross section of the posts, but the most interesting effect of the ice — polished tops on the basalt columns. Here, the column ends are exposed like a tiled floor and exhibit parallel striations where the glacier dragged rocks across them.
Rainbow Falls
Two miles downstream from Devils Postpile, the San Joaquin River tumbles over an abrupt 101-foot drop, sending rainbows of color into the mist. After the easy, 1.5 mile walk to Rainbow Falls from the Red's Meadow area, the roar of the falls and the refreshing mists invite you to stay awhile and enjoy a picnic lunch. Be sure to bring your camera-midday, when the sun is highest, is the best time capture rainbows in the mist.
The Devils Postpile and Rainbow Falls / or Reds Meadow is located 10 miles past Mammoth Mountain Ski Area's Main Lodge, on Hwy. 203. A mandatory shuttle bus is required during the busy summer months and departs from the Mammoth Adventure Center and new this year, The Village.
Proposed Fee Change for Reds Meadow This summer the Forest Service is actively seeking comments and feedback on a proposal to change the fees.. Learn more
General Management Plan (GMP) Devils Postpile National Monument is charting the course for management, resource protetection, and visitor use in a new General Management Plan.
