Devils Postpile is a dark
cliff of columnar basalt near
Mountain in extreme
northeastern Madera County in eastern
The longer fragments of basalt at the
base of the cliff are much larger than a person.
The postpile was created by a lava flow
sometime between less than 100,000 years ago (according to current
700,000 years ago (according to other dating methods). The source
of the lava is thought to have been somewhere near Upper Soda
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
later removed much of this mass of
rock and left a nicely polished surface on top of the Postpile with
very noticeable glacial
Postpile was once part of Yosemite National Park, but discovery of gold near
Lakes prompted a boundary change that left the Postpile
on adjacent public land.
proposal to build a hydroelectric
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
area into a United
States National Monument
. The John
and Pacific Crest
pass through the monument.
Basalt column on side
The Postpile's columns average in diameter, the largest being , and
many are up to 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
thing that places the Postpile in a special category is the lack of
stones from the Devil's Postpile can be seen at the entrance to the
United States Geological
Survey headquarters lot in Reston, Virginia.
Although the basaltic columns are impressive, they are not unique.
Basalt columns are a common volcanic feature, and they occur on
many scales (faster cooling produces smaller columns). Other notable sites
Causeway in Northern
Cave in Scotland, the Garni gorge in Armenia, the
Cyclopean Isles near Sicily, Devils Tower National Monument in Wyoming, Sheepeater
Cliff at Yellowstone National Park in Wyoming, Basalt
Prisms in Hidalgo, Mexico, the "Organ
Pipes" formation on Mount
Cargill in New
Hill in Mumbai, Organ Pipes
National Park in Australia and the
"Columnar Cape" (Russian: Mis Stolbchaty) on Kunashir, the southernmost of the Kurile Islands in Russia.
Ancient columnar basalt can be seen in a high desert dry river
falls area just north of Lajitas, Texas. The columns are accessible
on horseback, on foot, or mountain bike via trail .
Rainbow fall at Devils Postpile
- Roadside Geology of Northern and Central California,
Alt, Hyndman (Mountain Press Publishing Company, Missoula; 2000)
- Official NPS
- The Devil's Post Pile, Popular Science monthly, Feb 1916, page 178,
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