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You are browsing the archive for california Archives - Page 2 of 11 - Mountain Beltway.

27 September 2019

Friday folds: O’Shaughnessy Boulevard, Glen Canyon Park, San Francisco

The western edge of O’Shaughnessy Boulevard, near Glen Canyon Park in San Francisco shows beautiful examples of crumpled cherts. Here are a few dozen photos of these glorious outcrops, and instructions on how to visit.

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30 August 2019

Friday fold: Calafia State Beach

The Friday fold is a guest contribution to “Mountain Beltway” from the manager of the AGU Blogosphere, Larry O’Hanlon. It shows apparent crumpling of a few sedimentary layers at the toe of a soft sediment slump at Calafia State Beach in southern California.

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31 May 2019

Friday fold: Point Arena, California

It’s Friday, and I’m grateful that Bret Leslie of the NRC has stepped up with a Friday fold contribution from coastal California: Bret says this outcrop is: from my trip last month to the Sonoma and Mendocino coast. The first is the cliff below the Pt. Arena lighthouse. The marine deposits (now a marine terrace) are unconformably on top of the folded Miocene sedimentary rocks in the second photo. Here …

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3 May 2019

Friday fold: Monarch Canyon

When a dike is subjected to shear, how does it deform? A guest Friday fold from Darrel Cowan of the University of Washington teaches a nice little lesson. Join the field trip in Monarch Canyon of Death Valley National Park…

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26 April 2019

Friday fold: Black Sands Beach

The Friday fold can be found in a boulder of gray chert layers on Black Sands Beach, at Marin Headlands in California.

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19 April 2019

Friday fold: Angel Island “III”

For the third Friday in a row, “Mountain Beltway” features folds from Angel Island, in northern San Francisco Bay, California, This time, it’s meta-cherts on Perles Beach, showing impressive metamorphic recrystallization reactions.

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12 April 2019

Friday fold: Angel Island “II”

Happy Friday, all. Here are a few shots of crinkled, thin, multicolored cherts from Kayak Beach on northern Angel Island, California, piggybacking on the folds I showed you last week.

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5 April 2019

Friday fold: Angel Island “I”

The Friday fold is on the north shore of Angel Island, San Francisco Bay, showing blueschist-facies high-contrast metalliferous cherts with folds on many scales.

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29 March 2019

Friday fold: Plunging Purisima

AGU’s Centennial year is also the 35th anniversary of the publication of Clyde Wahrhaftig’s unique field guide to the geology of San Francisco. A team of geologists is updating “A Streetcar to Subduction” for a modern digital audience, and recently did some California field work to visit key sites. Check out one of them here with the Friday fold, as we visit a plunging syncline in the Purisima Formation on the coast near San Mateo.

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14 December 2018

Friday fold: Titus Canyon Anticline

A guest Friday fold brings us to a position in the sky somewhere over eastern Death Valley National Park. Join us in contemplating the Titus Canyon Anticline.

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