Once part of California's Yosemite Park, the Devils Postpile returned to protection of the National Park System as a nation monument in 1911. The park's rock formations of columnar basalt were formed from a plug of cooling lava nearly 100,000 years ago. During the last ice age, glaciers flowed down the Middle Fork of the San Joaquin River, carving away one side of the Postpile, exposing these uniquely shaped, three to seven sided columns. Frost wedging has pealed off rows of these columns over time, giving visitors a close-up look at these rock oddities.
Further south along the San Joaquin River is another reason for the park's popularity, Rainbow Falls. This 100 foot waterfall crashes off a cliff of volcanic rock, creating a rainbow in the mist with the midday sun.
Visitors to the park are first greeted with an overlook to the Minaret Vista, then a narrow, winding road, one-lane in places, leads down to the Devils Postpile, Reds Meadow, and the Rainbow Falls Trailhead. Mandatory shuttle bus service reduces traffic congestion and parking problems. More and more parks are moving to shuttle buses, an eco-friendly method of park transportation.