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USGS Geology in the Parks

Devils Postpile National Park Geologic Story

Devils Postpile
Photos by Wymond W. Eckhardt, NPS.

Top of the Postpile

A hike to the top of the Postpile reveals not only a cross section of the posts, but interesting effects of the ice- the polished and scoured tops of the rock columns. The polygonal column-ends are exposed like a tiled floor, and exhibit shining surfaces where the ice polished them with fine silt; parallel striations and grooves show where the glacier dragged rocks across them.

When the last glacier melted away, nearly all of the upper surfaces of the exposed rock in the Monument must have exhibited glacial polish. Now, however, weathering and subsequent erosion have removed almost all of the original polished surfaces, and only patches such as those on top of the Devils Postpile remain. (in such a context, the regulation prohibiting the collection of rock specimens in the National Monument becomes especially meaningful. Without realizing it, collectors could remove the most dramatic proof that a glacier rode over the top of the Devils Postpile, thus, not only destroying scientific evidence but detracting from the understanding and enjoyment of future visitors).

Continue to Curved Columns, See the Contents or Return to the Beginning

Material in this site is adapted from a pamphlet, Devils Postpile Story, by N. King Huber, USGS, and Wymond W. Eckhardt, NPS. It is published by Sequoia Natural History Association, Sequoia Natural History Association, HCR-89, PO Box 10, Three Rivers, CA 93271-9792, Telephone (559) 565-3759.


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