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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.


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.


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.)


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 …


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!


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.


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!


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.


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!


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: [gigapan id=”185784″] Link Here’s the flip side of the same sample, with a lot of fenestrate bryozoans to see: [gigapan id=”185809″] Link Fault breccia from the Corona Heights Fault of San Francisco: [gigapan id=”185868″] Link Amygdular metabasalt from the western Sierra Nevada of California: [gigapan id=”185894″] Link …


19 February 2016

Friday fold: Catalina Island #3

Happy Friday – sorry to have not shared any folds with you last week. I hope these beautiful folds in Catalina Island meta-cherts will make up for it: As with the previous couple of Friday folds, this image is courtesy of Sarah Penniston-Dorland (University of Maryland, College Park).


5 February 2016

Friday fold: Catalina Island #2

Happy Friday! Here’s another fold from Catalina Island, California – an antiform in metasediments, courtesy of Sarah Penniston-Dorland of the University of Maryland:


29 January 2016

Friday fold: Catalina Island #1

My friend Sarah Penniston-Dorland, of the University of Maryland, supplied this week’s Friday fold. it comes from Catalina Island, California, where Sarah just wrapped up some field work with two of her students. All three of them have given me permission to post the images here: The Catalina Schist is a suite of subduction-related metamorphic rocks. These rocks are amphibolite facies gneisses, but part of the Catalina Schist. The metamorphic …


6 January 2016

Slumped boulder on Marshall’s Beach, San Francisco

The week before the AGU Fall Meeting, San Francisco experienced heavy rain and strong coastal wave action. These two phenomena liberated a big boulder of serpentinite on Marshall’s Beach. As it moved downhill, it opened up a scarp with views into the colluvial soil horizons.


29 December 2015

Serpentinite mélange on Marshall’s Beach

South of the Golden Gate Bridge in San Francisco, there are beachside exposures of serpentinite mélange: tectonically sheared-out former oceanic crust accreted to western North America as part of an accretionary wedge.


28 December 2015

Corona Heights Fault, San Francisco

At the end of the AGU Fall meeting, Callan visits the Corona Heights “mirror” fault, renowned for its gorgeous slickensides. Explore the site in photos in GigaPans.


2 October 2015

Friday fold: cherts at Mount Diablo, California

My former student James O’Brien recently moved out to the left coast, and posted some photos earlier this week of a hike he took at Mount Diablo State Park in the mountains east of the San Francisco Bay area of California. There are some classic-looking Franciscan cherts exposed there, as these folded examples show: Seeing these pictures reminded me of the “GoSF” series I wrote last time I went to …


19 December 2011

Monday Geology Picture: Salt Flat Reflections in Death Valley

Well, I still haven’t had time to write up a substantial blog post. I spent this past weekend writing my thesis, wrapping Christmas gifts (how can it possibly be Christmas next weekend?), writing Christmas cards (and wedding thank-you cards! Finally!), and spending some time with my husband, who arrived home unexpectedly yesterday. He’s been at sea on a sampling campaign, but there’s some trouble with the ship, so he’s home …