Random Roadcuts, Episode #15: Learn Geology At An Interesting Roadcut On US 20 In Southern Idaho 

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I pull over for road cuts! My first fossil, a brachiopod stuck in a small chunk of limestone matrix, I found in a roadcut in the middle of the New Mexico desert. It really got my young 13 year-old mind thinking questioning how a seashell ended up in the middle of the New Mexico desert

You and "Crime Pays, Botany Doesn't" should do a collaboration where you pick a spot like this and both of you do a video exploring it. I'd love to see what you see differently...

Love these roadcuts and it's always a bonus when Shawn treats his viewers to a gnarly but not-too-spicy scramble!

I may not watch every single video, but I'm never disappointed when I tune in, especially for the Random Roadcuts! I really like that you're seeing the rocks for the first time with us. It helps knowing the process you go through to make your speculations and identifications. Plus, not a lot of people watching would look at a vertical wall surrounded by rubble and scree and say it's not too "spicy" to scramble up while holding a camera on a stick!😂 Thanks for another great adventure in geology, Professor!👏👍🏻

2:00 You said "here's a good gap in the traffic" and _immediately_ a truck and trailer whizz by and it scared the crap outta me. Thought you were about to get mowed down -- "Here's a good gaKABOOM!"

Geologist and part mountain goat! Well I got the first part of the video correct, so I'm learning more than I thought. Thanks Shawn.

You crack me up! “TaDa!” We made it to the top! I wish I could completely convey to you how interesting your videos are and how much I enjoy them! Thank you!

It’s gratifying to see even a geologist get tongue-twisted over “aluminum”! 😂 As always an enjoyable and informative video. If you’d told me back in October I’d be looking forward to videos on road cuts I’d never have believed you, but I most certainly do now! Thank you!

Thinking about the violent birth of that road cut is truly amazing. Thanks, Shawn.

Another comment not about this roadcut particularly, but to really encourage viewers to watch your rocks and minerals series *again if it's been awhile *... It's amazing what I continue to learn by review! Really, thank you, Shawn, so much.

I grew up in Fairfield. It's amazing to hear you dissect that road. So much we drive next to and know so little about it.

Every time I am amazed how much detail there is in the most unassuming road cut. As always, in your debt !

I traveled that road many times in years past and hadn't a clue about the geologic history it revealed. Thank you for a great lesson!

Loving this series Shawn. It's great fun to "read" along too. Thank you Sir!

Perfect end to my day…Random Roadcuts! Awesome. Thank you.☺️

@shawnwillsey I love the Random Roadcuts series! There is always more than what meets the eye and I love that you explain it so well, in a way that non-geologists and curious people like me can understand - thank you very much for that. It is the next best thing to actually going there :)

My mum would say, “Be careful crossing the road!” Xx

Layers and layers of rock.Layers of history.🤔 Thanks doll😉

Lot of memories for me on Hwy 20 and that 28 mile long straight stretch. I hit 108 mph on that stretch in a 1964 Dodge Dart as a high school student on the way to Sun Valley. This was our families' route to Redfish Lake from Mtn Home AFB where we summered for several years. Thanks for featuring this spot for in all the years present in the area I never learned much about what was under my feet and where it came from.

Thanks shawn, keeping the rocks alive.

Im always happy to see a Road Cut!

Love the Random Roadcuts series! Geology plus travelogue plus climbing = a fun and interesting experience.

Appreciate all you do Shawn. Thanks for another road cut video.

It blows my mind that a giant hill was formed 5 million years ago when a volcano erupted and dropped so much ash it left a hill. Such a quick violent event leaving a record from so very long ago. Cool.

The great way to see a rock "road trip".

Thanks for another great roadcut! I learn so much every time you post one of these! Happy to say I was tracking with this one right from the start, so your lessons must be sticking with me now. :)

As a rockhound roadcuts in many places can reward you with nice specimens along with it's geologic history. Greetings again from Mike in the Philippines and thanks for the videos.

Fun roadcut! Definitely cool to see the tuff, ash, volcanic evidence. Thanks, Shawn! ❤

Another among many geology educational videos. Thanks Shawn ...............612 like ..........

Thank you Shawn. Very interesting video.

Great content Shawn , absolutely love these random road cuts. It's as you say in the video it helps us where ever we are in the world to understand what rocks and geological features we are looking at. Thanks you

Thank you so much. You are a fine teacher.

Thanks for the episode. I have been through that cut travelling along 20, hundreds of times over the decades, but I had no sense of it other than as a blur. Central Park and then a roadcut on Highway 20 east of Fairfield -- places I've spent considerable time in or travelled by repeatedly!

Family in Fairfield, will have to check it out!

Thank you for posting this

That was really interesting

Very good! 😊

Thanks!

I have my copy of Roadside Geology of Idaho on the table next to me. I’ve been reading about the three regions that come together in my neck of the woods, but I’m going to take a break and read about this area. Interesting to see such dark felsic rock that isn’t obsidian.

Most roadcuts usually have some tail-o-light.

Interesting, Prof Willsey. You picked some wild country to explore. You were fairly close to the Craters of the Moon National Monument. I drove that same stretch of US 20 in the winter of 1955, west to east (Oregon to Virginia) in my 5-year old Ford convertible. That was before the Interstate highway system was built. I drove through an intermittent snow storm, then picked up US 30 at Pocatello and ran into a full fledged blizzard near Soda Springs. My old convertible was mechanically reliable, but the wind whistled through the gaps around the cloth top - about froze my buns off. But I was young and adventurous in those days, lol! About the geology in the cut. . . . could the very thin top layer be wind-driven volcanic ash, post-eruption?

❓Shawn, do you know why that white layer of soft, ashy dirt hasn’t completely eroded away, after 5 million years? Is it lack of rain/wind erosion or does it form a resistant crust over the softest layers? Is there a way to tell how much may have already eroded? Comparison with other formations? ❓ Also, when your camera was pointed south(?) showing miles of empty highway, I thought you were joking when you said you’d “wait until there was a break in traffic” to cross the road. I almost jumped out of my chair when a huge truck and car immediately roared past from the other (north?) unseen direction. Oh, yessir, go ahead and please do wait, it’s no joke! 😂. Always happy to see Willsey alive and well at the end of every road cut episode. Thank you as always!!

Great explanation love these random road cuts I’m learning a lot about your geology and what to look for at home here as I travel in Australia

Enjoying the vids. Learning, and now almost think-saying what you are saying at the same time as you identify what geological strata etc is being viewed. So I am getting there, and almost becoming a little second nature - which means that I am learning, and have learned up the majority of all of the basic geological types.

Hey Shawn Just got a copy of 'Geology Underfoot in Southern Idaho'. I'm looking forward to reading about it and soon going there. Thanks.

Yikes..be careful out there...don't try this at home :) Very cool I called it based on your previous videos..may be learning something in my old age. TY

Wicked road it… great rocks thank you

I can mentally visualize an Etna-like eruption wherein the initial blast of lava rapidly covers the nearby land, creating the dark glassy base layer; as you ascend thru the fallout horizons, you would be seeing material that was launched higher and higher into the atmosphere. The scale of this specific eruption is probably much more epic, but that's what comes to mind. One editorial comment, if I may: please leave the end card information up longer, so it can be read and digested; I had to replay the ending and freeze for a few more seconds to read and take in the info. A lighter background would also make reading easier (higher contrast). Love the series! Thanks again.

Sawtooth National Forest lies to the north and the Magic Reservoir (man - made lake) from snowmelt to the south. During drought times the rocks seen in that reservoir are amazingly exact to what is in this cut less the top . We see 5.8 mya rhyolite flow, 5.6mya Pliocene Square Mountain basalt, 5.6 mya rhyolite ash flow tuff, 11.7 mya rhyolitic dome and less than 2.6 mya basaltic flows and sediments. Lots of stuff going on volcanic wise for quite some time in the last 6 million years! Nice investigation on this cut Shawn! See the paper : The Geology and Geothermal Setting of the Magic Reservoir Area by Struhsacker/Jewell/Zeisloft/ Evans Jr. (1982)

I agree with the comment about Crime pays but Botany doesn't. It could be a good colaberation. Your roadcuts are wonderfull. It reminds me of riding in the car as a child. I'd look at many roadcuts on family trips and wonder about how they were created. Once i grew older and had taken earth science, geology, as well as joining the geology and mineralogical society of Rochester. I came to recognize many of the formations. No matter what, roadcuts still hold my eyes and mind. Thanks 💥🎊💥💥👍

Great Thx!

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We can take the school class for a trip looking for Prof. Shawn petroglyphs. Is there any significance to the patterns you make with your hammer? All fun aside, still enjoy your scaling of random road cuts. Take care.

Oh, and next time you cross the road, please use the camera too to look both ways, I was on edge, lol.

Great lesson Shawn. At first glance I would have said that dark coloured igneous rock was basalt, the composition of the phenocrysts is critical in arriving at the correct answer. Is the pink feldspar orthoclase ?

Road side geology has this area as the magic caldera of the Yellowstone hot spot. 12-14 million years ago. Nearby lava flows 8 miles away are 4-6 thousand ago.

Thanks

Can you please make a pocket version of yourself that I can carry with me on EVERY loooong roadtrip I take with my husband? I cannot recount how many times I've seen some curious geologic feature or outcrop (as we sped by) and desperately wanted to understand what I was seeing. Reading the rocks always adds such richness to those journeys. My husband is nowhere near as intrigued as I am, so he just shrugs. Booo! 😊

Mafic and felsic! Oh my.

So the lower unit is dark because of the glassy texture, rather than composition? Thanks again for an interesting virtual field trip.

Great breakdown, I was thinking a lahar for a bit but the relative rates of fusing of hot ash sure is plainly explanatory- I'm shocked at what a huge "belch" of ash material this represents, the thickness of the blob-

So Hot spot or not? I think Yellowstone hot spot thank you stay safe ALL.

Its handy to see how they lie in the landscape.

My first thought was “ash-flow tuff” good place NOT to be around when it formed.

It seems like the plants would have a hard time getting a foothold

It's a surprise that the lower rhyolite is so dark. Why is that? Why is Poison Creek called that? You missed a chance to tell people to ask themselves how they will get up a slope AND ALSO ask how they will get down. Getting down, with gravity pulling on you and loosening rocks underfoot, can be harder and more dangerous than going up. Nonetheless, you did a good job, and I learned something.

..having observed uninformed and likely illegal mineral removal along a roadside in south central Alaska, where someone with a pickup truck and helper with shovels, had backed up to get some loads from there.. and probably did not notice or care this 'gravel' was not naturally occurring, there. The state of Alaska filled in a very muddy hill-slide with gravel embankment materials from elsewhere at great cost and effort. At least a mineral hammer, does not seem threatening to official passers by! While this latter-day excavator, appeared to know nothing of local geology; the state hired a good contractor who did a fine job, of hiding the fact this was a just a covered section road-cut; and not a large deposit of costly machine made broken rock roadbuilding gravels. As long term resident of south central AK and smaller villages along the few roads, I'm rather aware of resources and their source; when they are not local to the geography.. Too bad the roadside removal of taxpayer funded mineral deposits was not observed by someone in authority. A uniform and side arm would likely be good accessories, to help convince those who'd mine imported filler along State Road #1 and #9 on the Kenai Peninsula. Thanks for these nice video archives; first aware of your effort due to Geology Nick at CWU online lecture series. His educational style & yours, reminds me of my father, hired as early instructor before any campus, for UAA/Kenai -- from the front porch of our family house in Moose Pass area, in 1966.. Eventually he took the job offer, not that he didn't already have four or five other avocations in life. That he was even in AK, was a matter of personal exploration after experience of WW2 Europe, with curiosity of natural sciences and art. Dad eventually made a good living, talking to people as he always did; in wilderness & classrooms. Rather than hellish WW2 battlefields he'd seen, and as a USAAC veteran; and self-taught natural scientist, from Utah, who went on to teach five topics in AK; and fairly much wrote his own ticket.. Unconventional, independent; like outdoor scientists who also share what they know, and keep on learning more. Kinda a good addiction? Take care w/crossings and crossroads as you travel.. ~ from small town AK-USA!🇺🇸🌳❄🍄🐚💮

Indonesia tomorrow? Lol

??? If this is a road cut, shouldn't the other side of the road look the same???? Love your videos! Thanks for sharing 🖖😎

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