Today we went for a hike in Devils Postpile National Monument. The monument protects the Devil’s Postpile an unusual rock formation of columnar basalt (1st and 4th pictures) and Rainbow Falls (2nd and 3rd picture), a waterfall on the Middle Fork of the San Joaquin River. In addition, it includes the John Muir Trail, the Pacific Crest Trail, and the Ansel Adams Wilderness.
Radiometric dating indicates that the the Devils Postpile formation was created by a lava flow at some time less than 100,000 years ago. Estimates of the formations thickness range from 400 feet to 600 feet. The lava that now makes up the Postpile was near the bottom of this mass. Because of its great thickness, much of the mass of pooled lava cooled slowly and evenly, which is why the columns are so long and so symmetrical. Columnar jointing occurs when certain types of lava contract while cooling. A glacier later removed much of this mass of rock and left a polished surface on top of the columns. The Postpile’s columns average 2 feet in diameter, the largest being 3.5 feet, and many are up to 60 feet long. Together they look like tall posts stacked in a pile, hence the feature’s name.
By the time we got to Rainbow Falls, the sun was behind clouds so we did not get to see a rainbow, but that was ok. After all that walking, Don needed a beer and low and behold Mammoth Lakes (a town near the monument) has a micro-brewery (last picture). The next to the last pictures shows part of Horseshoe Lake. The part of the lake in the picture is in an area that has high CO2 emissions that have killed the life around it. In the winter, people are advised not to go to this area and in the summer, only adults are advised to go there and to not stay long. Lots of interesting volcanic things still happening here.