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24 August 2018

Friday fold: Gneiss from Arapaho Pass, Colorado

It’s Friday, and I have another guest Friday fold to share: This one is from my Denver friend Greg Willis, who tells me it’s from near Arapaho Pass, near where we rain-hiked. Ahhhh, yes – a singularly soggy hike up in the Colorado Rockies. I remember it well, and it looks like Greg had better weather on this jaunt! Happy Friday to all!

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24 November 2017

Friday fold: Idaho Springs Fm. amphibolite

Here’s a guest Friday fold from reader Carl Brink: Carl tells me that this is: Precambrian Amphibolite schist float boulder from the Idaho Springs Formation in Rist Canyon west of Fort Collins, Colorado.  Knife is 2.25 inches long. Thanks for sharing, Carl!

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16 September 2016

Friday fold: Centenary migmatite

The Friday fold is a guest submission from Bill Burton, who took the photo of these lovely ptygmatic folds in migmatite in a national park on the 100th anniversary of the founding of the Park Service.

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2 September 2015

The Liar’s Club, by Mary Karr

I just finished this excellent memoir by Mary Karr, mostly about her childhood, mostly in east Texas. It’s not explicitly geological but it does feature an oil town economy and a hurricane, as well as some consideration of the Rocky Mountain Front Range in Colorado. I didn’t read it out of any illusions it would be geological, though – I selected it from the library shelf more from a desire …

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29 July 2015

Positively-weathering volcanic dike near Granby, Colorado

My friend Barbara am Ende sent along this lovely image of a dike in Colorado: Here’s the site. You can see the dike in Google Earth. Dikes are fractures, filled with molten rock, which then cools and solidifies, sealing the crack shut. In this case, once it got uplifted to Earth’s surface and exposed, the dike rock is tougher (more resistant to weathering) that the older rock it cut across. …

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13 February 2015

Friday fold: Ptygmatic Irving Fm., Colorado

Another one from Kim: Kim says: Pygmatic folds in the Precambrian Irving Formation. I think this is 1.7 Ga deformation, late in the Yavapai orogeny, which added various arcs in Colorado to North America. Good place to think about strain ellipses in progressive deformation. Zooming in on the best part, and dialing up the contrast a bit: That’s intense! Seriously strained rocks. What fun!

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6 February 2015

Friday fold: Ouray Limestone, Colorado

Kim Hannula shares a fold today: Kim says: The rocks folded here mostly the Devonian Ouray Limestone. There’s a fault through the outcrop, and another fault to the left of the photo. Regionally, the faults are mapped as normal faults, mostly with the east (right in photo) side down. Locally, that’s not what I see in this outcrop, which makes this a funky place to look at a fold with …

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26 October 2013

Off to GSA

This morning I’m on a flight to Denver, for the 125th anniversary annual meeting of the Geological Society of America. The annual GSA meeting is a special time of year for me, and for many geology professionals across the country. It’s an intense half-week of talks, sharing, learning, networking, hanging out with old friends, meeting new friends, getting inspired, and hopefully inspiring others. It’s a time to mentor our best …

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15 August 2013

Disconformity in northern Colorado

Have a look at this lovely (almost glowing) example of a disconformity between Coloradan limestone and overlying sandstone.

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14 August 2013

What do you see here?

Any observations? Any subsequent interpretations?

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