Random Roadcuts, Episode #16: Unravel the Geology of a Lonely Section of Idaho Highway 51

Learn to "READ" the rocks with this innovative video series designed to help you learn geology. Join geology professor Shawn Willsey and investigate a random roadcut, make observations, and formulate basic interpretations. Here in Episode #16, we explore a nice roadcut Idaho Highway 51 between Mountain Home and the Nevada border. GPS Location: 42.73158, -115.89825
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College of Southern Idaho
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[@shawnwillsey]

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[@RWBHere]

Maybe dumb questions, but why does that hill exist there, in isolation, with no obvious signs of folding and very few instances of faulting? Or are there folds/faults, which we cannot see, at each side of the outcrop? It seems to be far too friable for it to remain when everything around it has eroded. Thanks Shawn.

[@charleymitchell5461]

Can't wait, Hey Lake Idaho. Great story. I know so little..

[@mini30coupe]

Your narrative is refreshing. Years of learning brought to us very well. I learn your field with every search you do, thank you.

[@dancooper8551]

Love these roadcut videos. I first watch them with the volume on zero to test my observational analysis. I then rewatch them to see if I’m as smart as I like to think I am.😎 So far👍😅

[@shawnwillsey]

That’s a cool idea.

[@robertdiehl1281]

Random Toad Cuts are really enjoyable geology lessons. Something that is usually missed on a quiet drive through these beautiful areas.

[@richardwest9054]

Thanks, Shawn. Keep on driving and the Random Road Cuts coming.

[@kaytea2983]

Another great road cut and video. Thanks.

[@LisaBelleBC]

You are such a good teacher! I saw the fault before you said what it was! Thanks again for my fav random road cuts!

[@hestheMaster]

Ancient Lake Idaho is a very interesting thing to go over in the future. Seemed to be very active then not then again thoroughout the time it existed. This Saturday marks 44 years since Mt. St. Helens erupted. ( May 18,1980)

[@sandrine.t]

Volcanic ash: that's what I thought before you said it :) A wonderful explanation as always, really learning a lot with your Random Roadcuts! Thank you, Shawn! Hope you've having a great time in Iceland :)

[@rogerharris8081]

This past week we’ve been on vacation and travelled along 189 which follows Provo river. There is a massive fold (syncline) that is absolutely beautiful! I’m sure you have seen this in your travels.

[@hardrockgirl5844]

I love these !

[@jackienaturelover9761]

What a very interesting road cut. Really enjoyed it. Thanks for sharing.

[@joannekellam191]

Awesome road cut episode! Thank you!

[@LouinVB]

You were 3-4 km away from the Bruneau Woodpile petrified wood collecting site that I often visit. I know this road cut you are featuring as I have stopped to look at it before

[@JasonBower-ql3cd]

Hello Prof. From Lincoln, Nebraska 😊

[@Riverguide33]

Always surprised at outcrops that seem routine at a distance….but have a dynamic story to share. 👍

[@davidk7324]

Suggests widely fluctuating Lake Idaho levels over moderate geologic time? Ash à la mode.

[@Selah-dl3ef]

Thanks Shawn 💫

[@christinedaly2694]

Thank you Shawn great information can’t wait to see yr videos on Iceland

[@DrGeorginaCook]

Interesting thanks. Virtual field trips are great! Don’t get to see a lot of young geology where I live in Scotland. Rocks here just a billion years or so 😂

[@rickfranz5054]

Very cool outcrop!

[@JorgeSanchez-uk4cb]

Good morning Professor we have unrest at San Andreas at Bradley. We got some swarming Have a nice day 😃

[@MyMemphisable]

Thanks!

[@Darisiabgal7573]

Actually it kind of a cool road cut, the most stylish mudstone I’ve seen yet.

[@valoriel4464]

Thx Prof ✌🏻 fascinating geo-adventure

[@maryt2887]

Great road cut video! I am always amazed at what you find in these places. I started thinking about docent-led art talks that I have attended. Helps one to notice the little features that a cursory look misses.

[@YouTubalcaine]

I'd love to dig into that gravel bed to identify those cobbles and try to figure out where they came from. The variety of stone types suggests they were sourced over a large area, and they're all eyewitnesses, so to speak, to what seems like an interesting page of the lake's history. It must have been quite an impressive flood to behold.

[@Ferda1964]

Road cuts of the West are great spots to investigate the rocks even with only some basic knowledge of geology.

[@ThomasEckhardt]

Neat cut, thanks Shawn! Looks like some nice vertical bioturbation in the sandstone layer below the ash deposits?

[@briane173]

Windy-ass day that day, wow! Once we get schooled on Lake Idaho we should then be able to determine whether that road cut was strictly a stream environment or was along/below a shoreline given the alternating beds of sands and muds. Looking at the background it looks _fairly_ high in elevation compared to the SR Plain, maybe 2-300 ft. So hard to know if that section was ever below lake level or just above it.

[@J0hnC0ltrane]

Using google your at the Bruneau-Grand region of western Idaho. One site places the the beginning of the development at 16 million years ago while the usgs site says 12 million yrs. ago which might be the Middle Miocene. Just a guess and a google search. Thank you for the video Shawn.

[@harryromo2508]

Very interesting. I was looking for signs of Bonneville deposits, but didn’t see them. I think you’re higher than that.

[@raenbow66]

Exciting roadcut! Any attempt that you know of to estimate the length of time it took to accumulate it all? Thanks, Shawn!

[@samuelbess3038]

Fascinating...no mention of direction of flows origin of the sedimentary materials, generally said volcanic depisirion...no mention of rapidly of depisition.. type of fault?....clearly after all sedimentary and volcanic layering ended...why nothing continued?

[@Joe-Skier]

I'm thinking there were alot of fluctuations in the lake. Lake rises, lays down a mud layer. Lake drops, streams go farther into lake depositing sand. And the process repeated many times

[@johnlord8337]

With all these wet expansions (floodings ?) and retractions (massive droughts and drying up with windblown sands ?) of this Lake Idaho, especially with the mudstones, ... wouldn't there be the possibility of organic life, and freshwater or saltwater critters (even if down to diatoms and plankton) finds in these layers ?

[@7inrain]

How can we differentiate between ash layers that had been laid down on dry land and those being deposited in a lake? The ash layers you showed at @12:25 looked like they were well cemented together and they even withstood gravity, with some parts of the layer beneath it missing. Is this the mark of an ash layer deposited in a water body or am I wrong here? Thanks for another interesting video.

[@robtippin9111]

😎

[@clydecessna737]

...so is that fault or offset evidence of an ancient earthquake? [Great stuff as always.]

[@robmagee100]

Love the road cut explorations! When I was looking at some of the sandy layers with angular variations within the layers, the word “varves” came to mind… Is that off-base? I guess I don’t have a solid idea of what a varve is… I’m thinking it is an indication of change of deposition direction/current?

[@briane173]

They could indeed be varves, at least on a small scale. Varves are typically laid down seasonally whereas rhythmites usually form from large slackwater deposits from a flood or something like it -- large quantities of silts or muds sinking down to the bottom of a lake that didn't have much in the way of inflow or outflow for a period of time.

[@eaglepursuit]

That 12 inch thick sand layer at 11:30 in the video... were those vertical-ish marks towards the top ancient burrows in the sand?

[@causewaykayak]

Like worm burrows are they not ? Well spotted 😊

[@nickmcgarvey6463]

Shawn, I want to tell you about a road cut in the middle of nowhere but not that far from you. What's the best method?

[@oakhillclassroom4827]

When and at what point as a geologist? Do you finally talk about the liquid model sun ????

[@LynnMorgan-fh2re]

Is there a possibility that the bedding angle in some of the sand layers may indicate wind deposits?

[@shawnwillsey]

cross beds are very low angle so likely stream vs wind.

[@williamedwards1528]

Shawn: Would you say that that each of those very thin layers might be single day up to a seasonal accumulation of sediments?

[@georgepeck9288]

Can estimate the time sequence here? How duration does each distinguishable layer represent….seasonal or finer?

[@markuschampos5750]

What's the timeline for each layer? Is it possible to determine that?

[@anitapaulsen3282]

What might have caused the fault? Earthquake?

[@skyedog24]

Wouldn't you know it the loneliest road that you've talked about and I know this one 🤔😂

[@johnlord8337]

Glacial Lake Idaho - or - Lake Missoula ?

[@shawnwillsey]

Lake Idaho. We are way too far away from Lake Missoula with huge mountains in between

[@TorfinnBrekke90]

Plise luck at Italia super vulkano

[@wclugston]

Thanks!

[@shawnwillsey]

Thank you Bill!