1 January 2020

2019 Yard List

New year’s day! For this blog and me, the first day of the year is time for the annual recap of birds seen on my land in Fort Valley, Virginia. Here are the previous iterations:

This year’s list (biggest year yet!), in chronological order of first sighting:

  1. Pileated woodpecker
  2. Tufted titmouse
  3. Red-tailed hawk
  4. American goldfinch
  5. White-breasted nuthatch
  6. Red-bellied woodpecker
  7. Mourning dove
  8. Carolina wren
  9. Yellow-bellied sapsucker
  10. Chickadee
  11. Dark-eyed junco
  12. Downy woodpecker
  13. Hermit thrush
  14. Brown creeper
  15. Raven
  16. Turkey vulture
  17. Golden-crowned kinglet
  18. Purple finch
  19. Pine siskin
  20. Wild turkey
  21. Eastern phoebe
  22. American crow
  23. Sharp-shinned hawk
  24. Pine warbler
  25. Eastern bluebird
  26. American robin
  27. Whippoorwill
  28. Brown-headed cowbird
  29. Flicker
  30. Chipping sparrow
  31. Northern cardinal
  32. Harrier
  33. Blue-headed vireo
  34. Blue-gray gnatcatcher
  35. Ruby-throated hummingbird
  36. Red-eyed vireo
  37. Canada geese
  38. Broad-winged hawk
  39. Yellow-rumped warbler
  40. Ruby-crowned kinglet
  41. Ovenbird
  42. Bald eagle
  43. Fish crow
  44. Worm-eating warbler
  45. Scarlet tanager
  46. Barred owl
  47. Black-throated green warbler
  48. Great crested flycatcher
  49. Yellow-billed cuckoo
  50. Osprey
  51. American redstart
  52. Great blue heron
  53. Spotted towhee
  54. Wood thrush
  55. Black and white warbler
  56. Rose-breasted grosbeak
  57. Black vulture
  58. Brown thrasher
  59. Eastern wood-pewee
  60. Chimney swift
  61. Great horned owl
  62. Chestnut-sided warbler
  63. Blue jay
  64. White-throated sparrow
  65. Winter wren
  66. Swainson’s thrush
  67. Sandhill cranes (!!!)

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13 December 2019

Friday fold: blueschist & eclogite at Jenner, California

Here’s your Friday fold:

Let me explain. Like ~25,000 of you, I spent much of the past week in San Francisco, at the AGU Fall Meeting.

I headed out one day early, to capitalize on an opportunity to take a trip up to Jenner, California, to check out some cool metamorphic rocks on the coast there. My guide was Dexter Perkins, mineralogist and petrologist of the University of North Dakota. Dexter drove me up to the right place, but the weather wasn’t really cooperating:

Oh well, we’d come all this way: I guess we were going to get wet.

The resistant protrusions you see along the coast at Jenner poke out of the sand as well as the surface, and showcase truly wonderful rocks. Here’s a view of one of these outcrops, sticking out of the sand where the Russian River flows into the Pacific. Note also the birds (white things in the background): approximately the same number here as there were geophysicists at the Moscone Center a couple of days later!

This particular boulder is a relatively low-grade meta-basalt: it’s been altered to greenstone, but still preserves some primary igneous features. Here are two examples of well-preserved lava pillows in the greenschist-facies boulder:

There was more to be seen here, but we weren’t able to get to all the good stuff. For instance, this boulder of what appears to be mixed metamafic (green) and metapelitic (gray) mélange:

We couldn’t get to it because it was not quite low tide. The Russian River was thus backed up and covered in flotsam. That didn’t stop Dexter from trying to balance on floating logs to get to it (without success):

The muddy cliffs appeared to be dominated by metasedimentary mélange, with clear lozenges of graywacke in what appeared to be a shaley matrix. Here’s a chunk of the sandstone:

But the real attraction of the outcrops at Jenner are the high-grade subduction-related metamorphic rocks: blueschist and eclogite. Unfortunately, all my photos of these lovely rocks are sopping wet, leading to a lot of glossy glare… Still, the colors are something else:

Blueschist, as the name implies, is blue. The rock is blue because it has blue minerals in it: glaucophane and lawsonite. It’s a meta-basalt that recrystallized at high pressure but relatively low temperature. Because rocks are relatively poor conductors of heat, lithosphere can be subducted at a rate faster than it can thermally equilibrate to surrounding warm rock. This gives subduction zones a unique metamorphic signature: high pressure and low temperature are the conditions you need to get ~200° to ~500° C and depths of ~15 to ~30 km. Eclogites are meta-basalts, too, but they have been even further “down the subduction hatch:” perhaps ~45 to 60 km depth) with temperatures of 400° to 1,000° C. They have their own distinct color scheme: like a Christmas tree, with red garnet and green omphacite.

You can see both at Jenner, which is just about mind-blowing: that these rocks have been SO FAR down into the planet, and yet somehow, in spite of their density, made it back to the surface where lucky Subduction Pilgrims like myself could visit them and get to know them.

Here’s a diagram my colleague Christie Rowe drew up to explain blueschists for a stop on our new digital field guide to the geology of Angel Island, part of the Streetcar 2 Subduction project that we launched at Fall Meeting:

There’s really no precise cut-off between the two metamorphic facies, since the presence or absence of water will have a critical role in determining whether metamorphic reactions can proceed efficiently.

The blueschists at Jenner are unique in my experience, because they feature quite a lot of garnet.

This garnet’s presence in the blueschist is cited as evidence that these rocks were once all eclogite, and then some of them retrograde-metamorphosed to blueschist on their way back up to the surface.

Layering of blueschist layers relative to greenschist layers was a key feature of one boulder:

These cm-scale stripes are a little surprising – it’s not as if the green slices have been down to eclogite-inducing depths, but the blue ones haven’t. Something else is controlling the situation here, probably water, perhaps percolating along fractures in the meta-basalt.

It was in this one that the fold (that started this post) appeared:

I resolve to get back to Jenner when the weather’s more conducive to careful study of these intriguing rocks.

In the meantime, the AGU Fall Meeting was a big success, and I look forward to next year’s gathering, as well as the associated field trips! Happy weekend to you, and if you’re still in San Francisco, have a safe journey back home.

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10 December 2019

‘Streetcar 2 Subduction’ is live!

This week marks the launch of a project I’ve been working on for a year and a half: “Streetcar 2 Subduction,” a revision of Clyde Wahrhaftig’s classic field guide to the geology of the San Francisco Bay area. Working with Jamie Kirkpatrick of McGill University (the project’s leader) as well as Christie Rowe (also from McGill), Kim Blisniuk of San Jose State University, and John Wakabayashi of Cal State Fresno, we used brand-new content creation tools in the web-browser-based version of Google Earth to make a series of digital field guides.

These field guides are combinations of Google Earth, Google Maps Streetview, photographs, diagrams, and video, with links out to additional resources in the textual description of each site. Google allowed our team early access to the tools, which allowed us to build the trips over the past six months as “trusted testers” and launch the revised guide only a week and a half after Google released the content creation tools to the public. We greatly appreciate their trust, and are quite pleased with a blog post they wrote and published yesterday about the project.

You can access the trips on a laptop via the Chrome browser, or you can use them in the field with your smartphone and the Google Earth app.

AGU supported the revision effort with Centennial funding, and also tasked AGU staff with assisting: Brandon Bobosink was the project manager, Jenny Lund did editing, and Derek Sollosi edited our videos. Each made valuable contributions to the project, and the scientists on the project are very grateful for their expertise. Our goal was to separate wheat from chaff, and to update the science, and most importantly to make the rich geological history of the Bay area more accessible to more people.

The launch coincides with a bunch of anniversaries:

  • the 100th birthday of AGU
  • the 100th birthday of Clyde Wahrhaftig
  • the 35th anniversary of the publication of the original guide

We’ve released 7 trips at this point, with another 3 due out next month. Each trip has between 2 and 30 sites where geological insights can be gained: vistas and outcrops, rocks and structures, landforms and history. The trips are all free, and will continue to be so in perpetuity. AGU has also made a PDF of the original guide available to commemorate the revision.

Here is a link to the landing page for the project, with links (under “Streetcar trips”) to the various digital field guides: Because that is a very long URL, we also made this short one for easier sharing:

To promote the launch of the guide, our team led two field trips on Sunday, one north to look at Franciscan complex rocks related to Mesozoic subduction, and another south to look at deformation along the traces of the San Andreas Fault and the Hayward Fault. Here’s the active tectonics trip posing in front of a sag pond developed along a right step in the right-lateral San Andreas Fault:

More than a hundred people participated in the two trips! We feel really good about that.

If you’re at the AGU Fall Meeting today, there are several Streetcar related activities:

Eos ran an article about the project a few days ago: and that’s a good place to learn some of the basics if you’re curious. They also published a rembrance of Clyde Wahrhaftig, the original Streetcar author here:

A piece on the project aired on the local ABC news affiliate last night:, in which Christie does a great job explaining our motivations, and the reporter, Liz Kreutz, does a great job walking people through how to use it.

KQED science also featured the project in a brief piece here:

More press soon, I hope… 🙂

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6 December 2019

Friday fold: a secret Santa rock exchange gift!

I participated this year in the Secret Santa Rock Exchange, wherein I shipped out a mystery rock to a random person, and got back a mystery rock from another random person. What fun!

My mystery rock has folds in it!

It’s from Matt Bruseke at Kansas State University. Check it out:

Matt writes that this is

a piece of the Silver City rhyolite, from the Owyhee Mountains, Idaho. The sample comes from a rhyolite lava and is ~16.0-16.3 Ma… I collected this piece while we were sampling the lava for geochemistry/petrography because of the 3D nature of the flow folding that is present in the rock… I couldn’t resist!

So cool! I can’t resist it either!

Some more photos of other faces of the sample:

Matt actually sent me two rocks: the second was a Kansan kimberlite, as a bonus. (That’s the advantage of USPS flat rate shipping – you can cram as many rocks in the box as you can fit!) The Secret Santa Rock Exchange is the coolest thing I’ve done in a while – I recommend it to all for the 2020 holiday season!

Happy Friday, Happy #AGU19, and Happy Holidays!

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22 November 2019

Friday fold: Noonday Dolomite in Mosaic Canyon

Because I’m putting together a field course for spring break 2020 to Death Valley California, I was looking through old Death Valley photos this week, from the last time I went to that special place. It was seven years ago! How time flies…

This one is in Mosaic Canyon, and was taken by my student Marcelo Arispe, a talented photographer as well as a talented geologist:

By the standards of this place, that’s a very large fold. The rock unit being folded is the Noonday Dolomite, a Neoproterozoic carbonate unit that exhibits gorgeous ductile deformation in Mosaic Canyon. The canyon offers a suite of folds on almost all scales and styles to bedazzle the geologically-inclined visitor. Previous Friday folds from Mosaic Canyon can be seen here and here and here and here.

Be well. Have a fine weekend!

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15 November 2019

Friday fold: two samples from Tennessee Tech

I spent some time in east central Tennessee last week, visiting the Earth Sciences department at Tennesee Technical University in their lovely newly-remodeled home on the main campus quad. In a hallway display case, they had many beautiful specimens on display to educate and inspire. Here are two lovely examples of folding.

Disharmonic buckle folding

Symmetrical kink folding (small chevron folds)

Terrific rocks to take us into a terrific weekend. Have a good one!

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12 November 2019

The Overstory, by Richard Powers

This is an interesting novel. The book came highly recommended to me from two friends who have literary and environmental sensibilities that I respect, and it won the Pulitzer Prize for fiction this year, which is an accolade worth noting – a validation of its quality. It is a story about trees, and about “radical” environmental activists who try to save them. I suppose it could be viewed as a bit of a mashup between The Hidden Life of Trees, by Peter Wohlleben and Edward Abbey’s The Monkeywrench Gang. But there’s more to it than that. It’s not rollicking and feckless like the behavior of Abbey’s quartet of cartoonish ecosaboteurs. (I note that one of them is a semiloopy Vietnam veteran, kind of like Abbey’s character George Washington Hayduke. The harmony is even more profound when you note Powers’ character is even named “Douglas,” in what I presume is a tribute to Doug Peacock, the supposed real-life inspiration for Hayduke.) The treehuggers in The Overstory have a passion that is paired with serene wondrous contemplation of the organisms they seek to protect. And there are an equal number of other key characters who are not party to arson or chaining themselves to trees: a married couple, a video game developer, and a scientist who writes a very Wohlleben-like treatise (“tree-tise?”). The sternest critique I can offer of the reading experience is that these other characters ended up mattering less to the central story than I thought they would. I expected all the various arcs of narrative to ultimately merge into a compelling twist, but instead the book’s various “branches” grew off in different directions, and though a few tiny connections were inserted, they were in no way substantial, and so ultimately the characters’ stories stood independent of one another.

Though the novel confounded my expectations in that way, I found it a very compelling book on another, more important level: It articulates clearly and powerfully the most astonishing aspects of the plants we share the planet with. Trees aren’t just “rocks that grow;” Powers’s characters (and, I suspect, Powers himself) see them as animate beings with intentions, social behavior, and perhaps even wisdom. Therefore our “harvesting” of them is an act with ethical consequences – or more to the point, an act that is unethical, both for the sake of the trees themselves and for the sake of the humans who benefit from the trees’ existence. And so the book is ultimately not just about trees, or just about this handful of characters, but about the human relationship to the natural world, and the self-defeating collective decisions of society relative to the natural systems that sustain it. The book plays out over many decades, and many American historical events are woven into the narrative arc – the counterculture of the 1960s, the Vietnam War, the “timber wars” in the Pacific Northwest in the 1980s and 1990s, the 9/11 terrorist attacks, the Occupy Wall Street protests, and more. Through it all, the trees grow, and are logged, and grow back, and succumb to disease, and grow back, and are razed, and grow back, on and on. Silently they watch humanity’s frenetic action. The characters grow, and are lopped back, and so they grow in a new direction, and they get lopped again, and they react anew, shedding damaged branches, taking on new forms as a consequence of their individual histories. Ultimately, I’m not sure where the novel left me… I think I expected a masterful conclusion that left everything crystal clear, but that wasn’t how this book finished up.

Perhaps it leaves me here, now, in late 2019, in American society, where our society prioritizes making money over the preservation of the organisms we share the planet with. I’m not interested in being an eco-saboteur, but I am interested in promoting appreciation of the natural world, of deepening my own understanding of natural systems, of promoting a human relationship with natural ecosystems that embraces conservation as a default approach, and deploys respectful harvesting and use of natural ‘resources’ where appropriate, where sustainable, where ethical. What to do in our situation is not straightforward or clear-cut, but it seems to me that the idea of preserving landscape and biota as precious needs to be given more priority, not less. This book is a counterpoint to the way American capitalism generally treats these ideas. For me, it acted as a personal confirmation that I’m not crazy for thinking this way.

A thought-provoker, I reckon. A book that will make you re-examine the world you live in.

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8 November 2019

Friday fold: Rist Canyon cobble

Reader Carl Brink from Colorado shares this image with us:

There’s a Friday fold hidden in there! Can you spot it?
(It’s the cobble in the exact center…)

Here it is:

This is the bed of Rist Creek Canyon in northern Colorado.

Carl writes,

The area I found the cobble in is mapped as Early Proterozoic quartzofeldspathic gneiss, often containing almandine garnet.

That is indeed what this appears to be; It’s a lovely sample of the local bedrock.
Nice find, Carl! Thanks for sharing.

Happy Friday, all!

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1 November 2019

Friday fold: Newfoundland beach cobble

This Friday’s fold is found in a metasedimentary beach cobble I found last summer in southeastern Newfoundland:

A lovely little “pocket fold,” it came home with me and is among the handful of “deskcrops” I keep in my home office.

Happy Friday and happy November!

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25 October 2019

Friday fold: Identity of a BIF

Darrel Cowan steps up with the Friday fold again this week: this time it’s a polished slab, mounted on a wall indoors at the University of Washington’s Department of Earth & Space Sciences; an elegant and informative piece of décor:

…and with Darrel for scale:

It’s so reflective that glare is a bit of an issue in photographing it!

Here, I’ll zoom in on the un-glare-besmirched portion of the image:

Here’s another view:

Darrel wants your help, gentle and geologically-informed reader. He writes,

When we moved into our renovated building in 2006, the contractors had left spaces in the walls to mount six polished rock slabs. I found and chose the BIF and my brother and I gave it to the department. The slab is about 4 x 8 feet. The red layers are chert, and the gray, magnetite with possibly some hematite. The folds are awesome, and one can easily see the different behavior of the chert and magnetite. The wholesale slab merchant calls it “Iron Red” and claims it came from India, although they could not substantiate its origin.

BIFs are present in many Precambrian terranes. A colleague suspects the slab it “itabirite” from Brazil. Can anyone more positively identify the source?

Can you all help Darrel out with a positive ID on this beautiful BIF?


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