The Devils Postpile used to be much taller than what we see today. Powerful erosive forces have been at work during the last 80,000 to 100,000 years carving, shaping and demolishing remnants of the lava flow. Freeze-thaw cycles help break apart the columns. Earthquakes knock columns down into the talus slope below. The river slowly eats away at pieces that fall into the water. But no force has left a greater footprint on the Postpile than that of glaciers. In fact, we wouldn’t even see the beautifully straight hexagonal columns hidden within the depths of the lava flow had glaciers not excavated the formation. Several distinct glacial periods have occurred since the Postpile was formed and each has dug deeper and deeper into the dense, heavy rock known officially as andesitic basalt. The last major glacial period ended about 15,000 years ago. Glacial polish and striations evident on top of the Postpile are from this last glaciation.
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 Reds Meadow area, the roar of the falls and the refreshing mists invite you to stay and enjoy a picnic lunch. Be sure to bring your camera—midday, when the sun is highest, is the best time capture the rainbows for which the falls are named.
The Devils Postpile and Rainbow Falls / Reds Meadow area is located 10 miles past Mammoth Mountain Ski Area's Main Lodge on State Highway 203. A mandatory shuttle bus is required during the busy summer months and departs from the Adventure Center at the base of Mammoth Mountain and The Village at Mammoth. Closed in winter.