Devils Postpile National Monument was once part of Yosemite National Park, but discovery of gold in 1905 near Mammoth Lakes prompted a boundary change that left the Postpile on adjacent public land.[citation needed] A proposal to build a hydroelectric dam later called for blasting the Postpile into the river. Influential Californians, including Walter L. Huber, persuaded the federal government to stop the demolition and in 1911, President William Howard Taft made the area into a United States National Monument.Devils Postpile itself is a dark cliff of columnar basalt created by a lava flow sometime between less than 100,000 years ago (according to current potassium-argon dating) to 700,000 years ago (according to other dating methods). The source of the lava is thought to have been somewhere near Upper Soda Springs campground at the north end of Pumice Flat on the floor of the Middle Fork of the San Joaquin River, from where it flowed to the site of the Postpile, was impounded by a moraine, and reached a thickness of 400 feet (newer estimate) to 600 feet (older estimate). In any event, 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 cool; the joints develop when the lava contracts during the cooling process. A glacier later removed much of this mass of rock and left a nicely polished surface on top of the Postpile with very noticeable glacial striations and glacial polish. The Postpile's columns average 2 feet (0.61 m) in diameter, the largest being 3.5 feet (1.1 m), and many are up to 60 feet (18 m) long. Together they look like tall posts stacked in a pile, hence the feature's name. If the lava had cooled perfectly evenly, all of the columns would be expected to be hexagonal, but some of the columns have different polygonal cross-sections on account of variations in cooling. A survey of 400 of the Postpile's columns found that 44.5% were 6-sided, 37.5% 5-sided, 9.5% 4-sided, 8.0% 7-sided, and 0.5% 3-sided. Compared with other examples of columnar jointing, the Postpile has more hexagonal columns. Another feature that places the Postpile in a special category is the lack of horizontal jointing.The flora and fauna at Devils Postpile are typical of the Sierra Nevada. The Monument contains animals and plants such as black bears, pine martens, mule deer, coyotes, quaking aspen, black cottonwood, alder, and willows, as well as many wildflowers, such as cinquefoil and alpine shooting star. Dark-eyed juncos and white-crowned sparrows are common in the summer.Just a 2.5 mile walk from the Ranger Station, Rainbow Falls is the highest water fall on the Middle Fork of the San Joaquin river. Plunging 101-feet down to the turbulent water below, the falls are aptly named for the many rainbows that appear in its mist throughout sunny summer days. We hiked 7 miles and 1100 vertical feet visiting all these features plus we also visited the Lower Falls of the San Joaquin. It was a very beautiful hike and we all were quite spent at its terminus. We had lunch at White Bark Restaurant in the Westin Hotel at Mammoth Mountain. IT WAS A VERY SPECIAL OCCASION AS WE CELEBRATED THE 27TH ANNIVERSARY OF THE WOLF MARRIAGE!!!!

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