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Image: Glen Canyon Park Chert Outcrop

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Description: Roadcut revealing Franciscan chert rock, Glen Canyon Park, San Francisco, California.[1] This type of chert contains the skeletons of innumerable radiolarian creatures. It is a sedimentary rock, and the visible layering is due to the occasional inclusion of shale layers as the rock was deposited over millions of years.[2] The shale weathers more rapidly than the predominant chert, so the weathered rock looks like a stack. The remarkable folding of the stacked layers indicates the tectonic forces on this rock in this past, which warped the original planar layers into the fantastic shapes they now present. The road in the foreground is O'Shaughnessy Boulevard, which was constructed around 1935. This roadcut presumably dates from that time.[3]
Title: Glen Canyon Park Chert Outcrop
Credit: Own work
Author: Eric A. Schiff
Usage Terms: Creative Commons Attribution-Share Alike 2.5
License: CC BY-SA 2.5
License Link: http://creativecommons.org/licenses/by-sa/2.5
Attribution Required?: Yes

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