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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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22 August 2018

Q&A, episode 5

A reader asks: “What is foliation and what makes it so important to the structure of rock?”
Callan answers with a lot of images of beautifully foliated rocks.

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10 August 2018

Friday fold: Gnarly chert from Spy Rock

The Friday fold is an outcrop of folded chert from the Franciscan mélange in Mendocino County, California. (It should look familiar to anyone who’s ever visited Marin Headlands near San Francisco.)

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6 July 2018

Friday fold: twisted turbidites at Usal Beach

Last week, I spent two perfect days camping with family at Usal Beach, in Mendocino County, California. Along the beachside cliffs there, I spotted plenty of lovely turbidites: graywacke and shale and a little bit of conglomerate that had been scraped off the subducted Farrallon Plate to help contribute to the bulk of the Franciscan complex. That accretionary process imparted some stresses on these deep-sea deposits, and in many places …

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25 June 2018

Mafic volcanics atop felsic instrusives: Sonora Pass, California

Sonora Pass, California, is a lovely place to examine a volcanic-on-plutonic nonconformity that spans about 80 million years of missing time. Let’s check it out on a photo-rich virtual field trip!

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23 June 2018

Deformed conglomerate of Frog Lakes, California

Fifteen years after mapping deformed rocks of the Sierra Crest shear zone system in the high Sierra, a family vacation brings Callan back to the pre-batholith metasedimentary rocks which show a pronounced strain.

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8 February 2018

A spectacular display of Earth science in the Alabama Hills

A detailed examination of an elegant photo of the eastern front of California’s Sierra Nevada, from the perspective of the Alabama Hills. How many different geologic phenomena can be packed into a single image? Let’s find out!

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10 November 2017

Friday fold: soft sediment deformation in California’s Castaic Formation

The guest Friday fold comes to us from the Miocene of California, deposited in a releasing bend basin along the San Andreas Fault.

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19 August 2016

Friday fold: marble, Kings Canyon, California

My friend Bill Burton (USGS, Reston) shared today’s Friday fold — Chevron folds in marble, Kings Canyon, California. Nice! Thanks for sharing, Bill!

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7 April 2016

New GIGAmacro images of rock samples

Another week, another batch of new images produced on my home-based Magnify2 imaging system from GIGAmacro. Leptaena brachiopod in (Mississippian?) limestone from Montana: Link Here’s the flip side of the same sample, with a lot of fenestrate bryozoans to see: Link Fault breccia from the Corona Heights Fault of San Francisco: Link Amygdular metabasalt from the western Sierra Nevada of California: Link Araucaria mirabilis gymnosperm cone fossil, from the Cerro …

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