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Because of its unusual 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 striation s and glacial polish .
Devils Postpile was once part of Yosemite National Park, but discovery of gold near Mammoth Lakes, California prompted a boundary change that left the Postpile on adjacent public land. A proposal to build a hydroelectric dam later called for blasting the Postpile into the river. Influential Californians, including John Muir, persuaded the federal government to stop the demolition and in 1911 President Howard Taft made the area into a national monument. The John Muir TrailJohn Muir Trail is a long distance footpath in the United States of America running 211 miles (340 km) from the Yosemite Valley to Mount Whitney. Much of the trail serves as a section of the longer Pacific Crest Trail. It is named for naturalist John Muir passes through the monument.
The Postpile's columns average 2 feet in diameter, with 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. In a perfect world all columnar joints would create hexagonA regular hexagon A hexagon (also known as "sexagon") is a polygon with six edges and six vertices. Its Schlafli symbol is {6}. The internal angles of a regular hexagon (one where all sides and all angles are equal) are all 120 °. Like squares and equilat-shaped columns, however nature isn't perfect; a count of 400 of the Postpile's columns gave; 44.5% 6-sided, 37.5 % 5-sided, 9.5 % 4-sided, 8.0 % 7-sided, and 0.5 % 3-sided. However, compared with other examples of columnar jointing, the Postpile has more 6-sided columns. Another thing that places the Postpile in a special category is the lack of horizontal jointing.
Smaller versions of the postpile can be glimpsed along US Highway 395 in the Owens ValleyOwens Valley is the arid ranching valley of the Owens River in southeastern California in the United States. The valley stretches for approximately 75 mi (120 km) between the Sierra Nevada on the west and the Inyo and White Mountains on the east. The moun. See also Devils Tower National MonumentDevils Tower is a geological feature located in eastern Wyoming that was established as the first United States National Monument in 1906. An important landmark for Plains Indian tribes long before Europeans reached Wyoming, Devils Tower was called Mateo and the Giant's CausewayThe Giant's Causeway is an area of 40,000 tightly packed basalt columns resulting from a volcanic eruption 60 million years ago. The tops of the columns form stepping stones that lead from the cliff foot and disappear under the sea. Most of the columns ar, in IrelandThe island of Ireland ire in Irish, Airlann in Ulster Scots) is the third-largest island in Europe. It lies on the west side of the Irish Sea, close to the island of Great Britain. It is composed of the Republic of Ireland in the south and Northern Irelan.