Having driven across the US multiple times, I love a good roadcut. I've stopped and looked at many, however I have never had such a thorough explanation or one as interesting. One of the events I've experienced happened in the 60'a out by Palm Springs. My family and I had walked out into the desert in the early evening. As we looked around, we noticed a black line across the sand. As we watched, it turned out to be a small earthquake moving toward us. We waited and let it lift us about 3 inches, then passed. I've been in much larger and more violent quakes since then, but that one stands out as a favorite. I think it's what triggered my love of geology.
This is so awesome! I'm 56 and went back to high school in Alberta Canada to upgrade my Chemistry, Math and Physics so I can enroll in Earth Sciences at U of A eventually. Your videos -as well as several other channels have fired me up and helped me to decide to pursue my dream of being a geologist! Thank you so much ❤
Hey there, as a 40's y.o. botanist and "cartophiliac", Im currently weighing my options for the same, a new life in geology. Like for you, Shawn is a huge part of my inspiration, too. Good luck to you, @laughingoutloud5742
Its never too late! I remember 40 years ago there was a guy on my Geology course (University of Manchester, UK) who was 63! He was also determined to fulfill his dream to. So keep at it. I'm sure you will succeed..
18:15 Where you're standing is where I last stood _60_ years ago on my family's first trip to Hoover Dam. At that age I was absolutely stunned at how tall the dam was above the river on the downriver side. The Interstate going over the bridge of course is brand new; back 60 years ago the only way across was over the dam on that narrow 2-lane road.
Thank you for taking the time to Annotate details in the video that may not be clear or that you wanted to add in supplement later in post. We Really Appreciate the clear effort and that goes into making these. Always interesting to see a enthusiasts take on places I have been, and places I almost certainly may never see IRL. Thank You Shawn!
Thanks again, you are amazing. I have wondered if you encounter any problems, i.e. snakes, insects, etc. Be safe, please, but continue to educate us. It is amazing. I am a young 70+, and I have always been fascinated by rocks, especially from the ocean. I have also wanted to travel to visit the dam, Yosemite, and the Grand Canyon. You have given me that opportunity from another perspective. Thanks again. We live in Maine, and the geological aspects are also amazing.
I was totally expecting almost all sedimentary rock around Hoover Dam, and instead it's all volcanic! The faulting and the dikes/sills running through the tuff is spectacular. Now I sit here shocked that they could construct such a sturdy dam out of mostly tuff near the top; I wouldn't consider that entirely stable. OTOH there's no shortage of igneous rock to cut into either.
"Fairly small crystals, so that indicates that the magma cooled slowly" 4:04 I thought it was the other way around and that slow cooling allowed for larger crystals to form. Shows that I have a lot to learn!
Always respectful especially when you are explaining things I have wondered about for many years. I ĺived in Las Vegas for over 55 years and dear old Dad lived in Phoenix so I have been over that Dam so many times. Thank you Sir.
When I lived in Henderson, NV, I spent countless hours exploring Lake Mead Rec Area and the Hoover Dam area. I was already a photographer but started seriously photographing geological points of interest (a number of those photos are now in use by the NV Bureau of Mines & Geology). There's a really amazing area behind the Hoover Dam Lodge leading to the Railroad Tunnel trail that to my eyes looked volcanic which I've always wondered about. There are stunning layers of black, red, orange and pinks. Makes me feel like I'm on another planet. I've also checked out this particular turn-out where you are here, but only briefly, as it's perilously close to traffic! Really loving this road cut series!
Yes - "super sweet"! Please keep 'em coming - really great fun. I find you're challenging me to interpret what you're showing us and I love it! Thanks again Shawn.
What a rich stop! I love seeing especially the tuff and slickensides, that confirm my thoughts. And clear fault delineations! Oh Wow! Gorgeous. "Not busy" ?? 😅 Thank you so much, Shawn! Awesome. ❤
❤🖍📙🇺🇸Dear teacher Swaml I'm sure your country have to be proud of you as a best teacher as a smart man and more representative geology professor now and forever. Great jobe you have done for us around the world. Thanks a lot from Brazil.🤝🖍📙🌹🇺🇸
Very interesting. We have a lot of tuff around where we live in the San Luis Valley. If you are ever in this area you should do the north side of Poncha Pass. It is crazy with all kinds of different rocks together with all kinds of intrusions from black to almost white.
Deep thanks Shawn! Having coffee with you…I had observed in the past (I’m 80) when I had my “miners licence” --these rock stories…. always excited me. I saw different fault and wondered at the chaotic directions. I had recognized tuft and found large layers in places that shocked me because there was no history of volcanos…..but once I started studying Mt S. Helens …I wondered if what I was viewing was wind directed to the area I was in….lower border area of BC
Like this one what I co-wrote: www.amazon.com/s?k=roadside+geology+of+idaho&hvadid=580626280500&hvdev=c&hvlocphy=9029448&hvnetw=g&hvqmt=e&hvrand=13979168904084571093&hvtargid=kwd-810629645&hydadcr=3205_13534113&tag=googhydr-20&ref=pd_sl_q39jhvkz8_e
I have been running into fault faces and slickensides and slicken lines for years without knowing what they are. They really are everywhere in the Basin and Range.
Thanks for this. Cool slickensides. 19:10 - the series of faults is similar in appearance to a large retrogressive slope failure, but with a different cause.
Thanks for exposing this, so to speak. I get to Vegas a few times a year, but haven't been to the bridge since it opened years ago. Need to go back and explore more now. Cheaper than an afternoon at the casino.
From Researchgate: "The Hoover Dam area contains exposures of Precambrian metamorphic rock, Tertiary volcanic and plutonic rock, and Quaternary gravels... Paleozoic rocks are restricted to roof pendants in Tertiary plutons and xenolithic blocks in mafic lava flows. With rare exception, rocks of the Hoover Dam area have been broken along numerous late Miocene faults with complex slip components and the Mead Slope left-lateral strike-slip fault... STRATIGRAPHIC UNITS PRECAMBRIAN Precambrian gneiss, amphibolite, schist, and pegmatite of the Lake Mead area are dated at 1.5 to 1.8 Ga (Volborth, 1973; Condie, 1982). Outcrops of Precambrian rock occur only in the southern map area. These outcrops are commonly intruded by the Wilson Ridge and Paint Pots plutons."-GEOLOGIC HISTORY OF THE HOOVER DAM 7.5' QUADRANGLE, James. G. Mills, DePauw University.
Love this series... There's an abandoned railroad cut in eastern Washington just off 95 adjacent to the Steptoe battle field that I'd like to see your reaction to.
I have to imagine this is one of the most studied rock exposures in the country considering what is built on top of it. Still I had no idea what kind of rock it was until today, thanks!
Thank you Shawn - that was great - I got onto street view in Google Earth and walked the rocks with you :) One thing I'm curious about, does the volcano still exist? or remnants of it? Where might the origin of those volcanic eruptions (lava, tuff, and ashfall) be? Seems like there was a lot of volcanic activity in that area, is that from subduction? Are there still active volcanoes in the Hoover Dam area? (I know about the volcanoes in New Mexico - are they related?) OK - I could ask questions all day, I'll stop for now. Thanks!!
It's basin and range out there, so not subduction, the cause is crustal extension. Thin crust relieves pressure on mantle below and causes melting, then that melted rock intrudes upwards through the faults created from the extension processes.
That was awesome. So much violent geological history on show in just a small area. From what must have been an enormous explosive volcano laying down a thick ash layer, then lava intrusions, and lots of seismic shearing. I particularly liked the view across the canyon where you could see the series of faults. Would those faults have gradually slipped over a number of earthquakes, or are they more likely to have been the result of one violent upheaval?
Thank you for the plethora of highly educational and informative videos. Your style of video is simple, clean, concise and keeps true to the subject matter.
Interesting faulting there, Shawn. Looking at the way it has been developing through the ages, it raises the question, 'From a geological viewpoint, was the Hoover dam built in an unsafe location?' That intrusion, which highlights all of the disjointed fault movement downstream of the dam wall, is rather concerning.
I visited Mt Lassen last week and found some slickenlines and slickensides in the rock at the Bumpass Trailhead Parking. I would have known what I was looking at had it not been for your great and informative video's. I was able to share this information with my grandsons. Thanks.
Wow, this takes some sort of road cut prize, lol. As your voice got excited near the beginning I was realizing that was a fault with the slickenlines. I got excited seeing all the different directions faults were going in such a small place. What a lot of dikes, too. I've only ever seen scenic shots of the dam area. I've never been near that area. that is really an interesting geology location. I wonder where all the ash that produced the tuff came from. For a slow day there was a lot of traffic still.
Very interesting. When you get slickenlines like that, can those be formed from a single event... fast movement along the fault, or does it need to be slower, small movements over a long period of time, like striations from a glacier?
Just fascinating, Shawn! It is mind boggling to see the immensity of it all. I've always wondered what a fault looks like inside, and your explanation of the side movement was very interesting. What would the rock look like if the motion had been up and down? Do you have that posted somewhere that I could look it up? Many thanks for this presentation! It was just long enough to keep us geology neophytes from overwhelm. You rock! 😄👍
I just followed your footsteps on the road cut with Google Earth “Street view.” Pretty cool. All of the views, none of the traffic! Over on the Arizona side there is a walk to “Liberty Bell Arch” that involves some “cross country” travel across bare rock. I found a really cool xenolith about the size of a bowling ball that appeared to be Paleozoic carbonate rock incorporated into the tuff. (It had pretty clear development of arid land type chemical weathering caused by rain-drop solution. If any viewers of this video are in the Hoover Dam area, opportunity to view a huge variety of rock formations is not to be missed.
You can support my educational videos by clicking on the "Thanks" button just above (right of Like button) or by going here: www.paypal.com/donate/?hosted_button_id=EWUSLG3GBS5W8 or here: buymeacoffee.com/shawnwillsey
On a spring break college field trip in 2002 we got lit up by homeland security at the railroad tunnel above the dam on the NV side. We had to sit while 1 student was escorted to the parking lot to bring the vans to some get us. We swear we didn't see the no trespassing sign
Another great Roadcut video! Not sure if this has been answered before, but how does the construction process alter what we might see? Would any of the fractures and coloration be accentuated by road construction?
I just watched your road cut video on Union Pass, AZ. Do you think the same eruption event that created the tuff here is the same that created the tuff at Union Pass, since they are generally in the same vicinity. Thank you for these videos, they are fascinating!
Looking at the amount of offset of those intrusions, near the end of the video, I have to wonder when the dam will be destroyed by an earthquake? Or how many earthquakes will it take to destroy the dam? Enjoy your videos! 😀
Thats a lot of tuft. I wonder how far it spreads out, or how far the ash flow spread from the volcano when it happened. How long did it last? Was it just one event that produced that much ash? How long after did the next basaltic intrusion happen? I always come away with more questions. lol Nice road-cut reveal. ;-)
I wonder about the inferred dike or sill and if one would take a series of thin sections at progressive distances from the contact, might there be some mineralogic evidence of thermal metamorphism? I.e., mineralogic zones correlated with temperatures. Of course one would have to be a better mineralogist than me. Also I am wondering if the force of the intrusion my have contributed to the series of local displacements that gave rise to all the slickenlined surfaces, particularly given orientations of the lines appear to be in different directions?
Are you familiar with the Red Rock area west of Las Vegas? There is a place in the Cottonwood Valley where there is an amazing display of geologic history going from undersea shinarump layers to shallow water layers including petrified wood to the Aztec sandstones, all within a stone's throw.
Hello again. The videos that you referenced above are of the Aztec Sandstone and the limestone overthrust. The area I'm referencing is the strata below the sandstone as it transitions from aquatic deposition (probably sub-sea) to shallow water (with petrified wood) then up to the dry land sand dune deposits. This is best seen in the Oak Creek area.
I think you've mentioned before about structures being built around potentially unsafe sites. With the faulting right up against the dam, would this not be a concern? Or is it because they are so old and unlikely to cause a problem again? Thx
Hi Prof. 1 question about slicken surfaces: are they the result of a long and slow movement of the rocks or Do they appear suddenly during earthquakes?
Ive heard the term (horizontal fault) I thought that was the jump the shark interpretation of the century.....then you walked right under a 40° uphill fault. Dont know if youvsaw that usually nothing gets by you. Im just wondering how motivated was that tuff !? I think i can i think i can
Thank you Professor Shawn for another amazing road cut. I have a question for you, is this area still seismic active because of all the faults in this area of the dam?
According to "Roadside Geology of Nevada" the tuff is "Tuff of Hoover Dam" and the authors do mention the dike cutting across the tuff. They describe the dikee as being compose of olivine basalt and basaltic andesite. Nick Zentner video streamed his first Geology 101 class after the 2020 closure live . The rock lab was taught by someone else so is not included and the class is centered on Washington state geology. I think that the geology community thinks of Nick as more of a knowledgeable presenter than a geologist. He acknowledges that when he puts his educator role as his strongest attribute over any research role.
Pretty sure he was talking about the tuff - that's sedimentary, stuff that accumulates by layers over time that isn't hot to the point of being liquid/flowing. Yes, there were volcanic rocks, but the tuff was the sedimentary rock he was referring to :) As he said, all three types of rock can be found in the Hoover Dam area. This was a great example of two of them right next to each other.
@@imbwildrd3693 Thanks for the clarification, that would have been ambiguous distinction to me also. If anyone could detail the nuance, how is a Pyroclastic flow defined then if it is distinct at all? Or is that possibly a spectrum of both and maybe defined in context? Possibly it is just a form of ash or tuff?
Tuff is a volcanic rock composed primarily of ash. In the video, I mention that the rock has the appearance of a sedimentary rock due to the clasts (rock fragments) when it is actually an igneous (volcanic) rock.
@@shawnwillsey Thank you for your reply. If you've identified tuft, or welded tuft, or whatever those rocks are, and they originated as volcanic ash, or by some other process of magma extrusion, or by whatever means that we categorize as "igneous," there is likely to be a history of volcanism in the vicinity. Can the source of the tuft be located, or has it eroded away?
Given all the evident faulting, how did the civil engineers decide this was a reliable site to build a high head dam? History has shown they made a good if risky choice.
Having driven across the US multiple times, I love a good roadcut. I've stopped and looked at many, however I have never had such a thorough explanation or one as interesting. One of the events I've experienced happened in the 60'a out by Palm Springs. My family and I had walked out into the desert in the early evening. As we looked around, we noticed a black line across the sand. As we watched, it turned out to be a small earthquake moving toward us. We waited and let it lift us about 3 inches, then passed. I've been in much larger and more violent quakes since then, but that one stands out as a favorite. I think it's what triggered my love of geology.
Always love those tilted power line towers, make me feel like I’m falling down.
This is so awesome! I'm 56 and went back to high school in Alberta Canada to upgrade my Chemistry, Math and Physics so I can enroll in Earth Sciences at U of A eventually. Your videos -as well as several other channels have fired me up and helped me to decide to pursue my dream of being a geologist! Thank you so much ❤
Wow. I am super impressed with your ambition. Go for it!
Hey there, as a 40's y.o. botanist and "cartophiliac", Im currently weighing my options for the same, a new life in geology. Like for you, Shawn is a huge part of my inspiration, too. Good luck to you, @laughingoutloud5742
@Nrc3neallyo OMG cartophiliac too!! Lol Cheers and same to you; who knows we might meet one day working!!
Its never too late! I remember 40 years ago there was a guy on my Geology course (University of Manchester, UK) who was 63! He was also determined to fulfill his dream to. So keep at it. I'm sure you will succeed..
18:15 Where you're standing is where I last stood _60_ years ago on my family's first trip to Hoover Dam. At that age I was absolutely stunned at how tall the dam was above the river on the downriver side. The Interstate going over the bridge of course is brand new; back 60 years ago the only way across was over the dam on that narrow 2-lane road.
Thank you for taking the time to Annotate details in the video that may not be clear or that you wanted to add in supplement later in post.
We Really Appreciate the clear effort and that goes into making these.
Always interesting to see a enthusiasts take on places I have been, and places I almost certainly may never see IRL.
Thank You Shawn!
Thanks again, you are amazing. I have wondered if you encounter any problems, i.e. snakes, insects, etc. Be safe, please, but continue to educate us. It is amazing. I am a young 70+, and I have always been fascinated by rocks, especially from the ocean. I have also wanted to travel to visit the dam, Yosemite, and the Grand Canyon. You have given me that opportunity from another perspective. Thanks again. We live in Maine, and the geological aspects are also amazing.
Thank you for your comments. I hardly ever see snakes and usually they are not venomous. Insects? Sure but rarely anything dangerous.
That was so interesting. I live in North/West Las Vegas and its always nice to learn about the Rocks beneath my feet as it were!
Welcome to Las Vegas! Silverado Ranch area here.
Aloha from SW Vegas!
Thank you for helping educate people beyond your classroom!!!
I was totally expecting almost all sedimentary rock around Hoover Dam, and instead it's all volcanic! The faulting and the dikes/sills running through the tuff is spectacular.
Now I sit here shocked that they could construct such a sturdy dam out of mostly tuff near the top; I wouldn't consider that entirely stable. OTOH there's no shortage of igneous rock to cut into either.
Great to see. Thank you, Shawn! Greetings from Iceland.
Been waiting for one like this. I love the variation along highway 93 through that canyon, from the Nevada side and Arizona side.
Oh nice, we build a huge Bridge over a heavily faulted surface. Great Video Thx!
Thank you always for your videos professor. Enyoyed the view, the welded tuff visuals and lesson.
The exposure in the canyon around 18:10 is beautiful !
Seeing that sill being offset faulted by that amount is stunning...
Another great video !
"Fairly small crystals, so that indicates that the magma cooled slowly" 4:04 I thought it was the other way around and that slow cooling allowed for larger crystals to form. Shows that I have a lot to learn!
Always respectful especially when you are explaining things I have wondered about for many years. I ĺived in Las Vegas for over 55 years and dear old Dad lived in Phoenix so I have been over that Dam so many times. Thank you Sir.
Now that's what I call a spectacular bridge ! Engineering at it's finest.
When I lived in Henderson, NV, I spent countless hours exploring Lake Mead Rec Area and the Hoover Dam area. I was already a photographer but started seriously photographing geological points of interest (a number of those photos are now in use by the NV Bureau of Mines & Geology). There's a really amazing area behind the Hoover Dam Lodge leading to the Railroad Tunnel trail that to my eyes looked volcanic which I've always wondered about. There are stunning layers of black, red, orange and pinks. Makes me feel like I'm on another planet. I've also checked out this particular turn-out where you are here, but only briefly, as it's perilously close to traffic! Really loving this road cut series!
Yes - "super sweet"! Please keep 'em coming - really great fun. I find you're challenging me to interpret what you're showing us and I love it! Thanks again Shawn.
What a rich stop! I love seeing especially the tuff and slickensides, that confirm my thoughts. And clear fault delineations! Oh Wow! Gorgeous. "Not busy" ?? 😅
Thank you so much, Shawn! Awesome. ❤
Love to see these videos, but.... no stopping means no stopping for anyone. Love these videos, and love your dedication to geology
Many interesting mining activities, lived there 20 years and liked panning some of the tailings. Interestingly many rare earth minerals to be found 😊
❤🖍📙🇺🇸Dear teacher Swaml I'm sure your country have to be proud of you as a best teacher as a smart man and more representative geology professor now and forever. Great jobe you have done for us around the world. Thanks a lot from Brazil.🤝🖍📙🌹🇺🇸
fantastic series! Thank you for bringing hands on geology with your knowledge insight and humor. Love it!
Thx Prof ✌🏻. Your vids are always great.
Very interesting. We have a lot of tuff around where we live in the San Luis Valley. If you are ever in this area you should do the north side of Poncha Pass. It is crazy with all kinds of different rocks together with all kinds of intrusions from black to almost white.
Very much enjoy your Random Roadcuts Series. Thanks
Close to the road, Shawn. I am going to start praying for you on the Random Roadcut episodes.
Deep thanks Shawn! Having coffee with you…I had observed in the past (I’m 80) when I had my “miners licence” --these rock stories…. always excited me. I saw different fault and wondered at the chaotic directions. I had recognized tuft and found large layers in places that shocked me because there was no history of volcanos…..but once I started studying Mt S. Helens …I wondered if what I was viewing was wind directed to the area I was in….lower border area of BC
Thanks again Shawn, great explanations, this reminds me so much of the old books we used to get in Calif "Roadside Geology of......."
Like this one what I co-wrote: www.amazon.com/s?k=roadside+geology+of+idaho&hvadid=580626280500&hvdev=c&hvlocphy=9029448&hvnetw=g&hvqmt=e&hvrand=13979168904084571093&hvtargid=kwd-810629645&hydadcr=3205_13534113&tag=googhydr-20&ref=pd_sl_q39jhvkz8_e
I have been running into fault faces and slickensides and slicken lines for years without knowing what they are. They really are everywhere in the Basin and Range.
As always incredible video! Love love love the random road cuts series! Thank you so very much!
Totally agree! Another fantastic and educational trip I'd never get to do in person...thank you, Professor!👏👏👍🏻👍🏻
Thanks for this. Cool slickensides. 19:10 - the series of faults is similar in appearance to a large retrogressive slope failure, but with a different cause.
Love your delivery! Presently Taking geology and can understand most of the terminology you use. Thank you so, so much!
Thank you for educating all of us.
Thanks for exposing this, so to speak. I get to Vegas a few times a year, but haven't been to the bridge since it opened years ago. Need to go back and explore more now. Cheaper than an afternoon at the casino.
Outstanding. Be careful!
i really love seeing the faults on the other side of the road just fascinating thanks
From Researchgate:
"The Hoover Dam area contains exposures of Precambrian metamorphic rock, Tertiary volcanic and plutonic rock, and Quaternary gravels... Paleozoic rocks are restricted to roof pendants in Tertiary plutons and xenolithic blocks in mafic lava flows. With rare exception, rocks of the Hoover Dam area have been broken along numerous late Miocene faults with complex slip components and the Mead Slope left-lateral strike-slip fault...
STRATIGRAPHIC UNITS PRECAMBRIAN Precambrian gneiss, amphibolite, schist, and pegmatite of the Lake Mead area are dated at 1.5 to 1.8 Ga (Volborth, 1973; Condie, 1982). Outcrops of Precambrian rock occur only in the southern map area. These outcrops are commonly intruded by the Wilson Ridge and Paint Pots plutons."-GEOLOGIC HISTORY OF THE HOOVER DAM 7.5' QUADRANGLE, James. G. Mills, DePauw University.
Love this series...
There's an abandoned railroad cut in eastern Washington just off 95 adjacent to the Steptoe battle field that I'd like to see your reaction to.
Great video at one of my favorite places to visit. And now I need to go back and really look at the rock formations closer!
What a great cut. When you retire you should start a geology tour company. I’d come from Australia!
I have geology tours now if you are interested. Regional trips around southern Idaho, a May 2024 trip to Iceland, and a 2025 Grand Canyon river trip.
Oh! Amazing! I’ve seen these formations driving by in the car. Appreciate your explanations of what I observed. Cool!!
Good job. Wonderful photos. I could see where someone took soil samples looking for gold, I bet.
I have to imagine this is one of the most studied rock exposures in the country considering what is built on top of it. Still I had no idea what kind of rock it was until today, thanks!
Thank you Shawn - that was great - I got onto street view in Google Earth and walked the rocks with you :) One thing I'm curious about, does the volcano still exist? or remnants of it? Where might the origin of those volcanic eruptions (lava, tuff, and ashfall) be? Seems like there was a lot of volcanic activity in that area, is that from subduction? Are there still active volcanoes in the Hoover Dam area? (I know about the volcanoes in New Mexico - are they related?) OK - I could ask questions all day, I'll stop for now. Thanks!!
It's basin and range out there, so not subduction, the cause is crustal extension. Thin crust relieves pressure on mantle below and causes melting, then that melted rock intrudes upwards through the faults created from the extension processes.
Not sure where the vent (source) of this ash is.
AWESOME! Thanks for this video. Greatly appreciated. 😊
That was awesome. So much violent geological history on show in just a small area. From what must have been an enormous explosive volcano laying down a thick ash layer, then lava intrusions, and lots of seismic shearing. I particularly liked the view across the canyon where you could see the series of faults. Would those faults have gradually slipped over a number of earthquakes, or are they more likely to have been the result of one violent upheaval?
I was there over40 years ago! I don’t remember much about the rocks unfortunately but I do remember it was pretty spectacular & hot 🥵
Looks like an excellent spot to build a dam
Thank you for the plethora of highly educational and informative videos. Your style of video is simple, clean, concise and keeps true to the subject matter.
I love the enthusiasm at all the little discoveries. Very interesting.
Interesting faulting there, Shawn. Looking at the way it has been developing through the ages, it raises the question, 'From a geological viewpoint, was the Hoover dam built in an unsafe location?' That intrusion, which highlights all of the disjointed fault movement downstream of the dam wall, is rather concerning.
I visited Mt Lassen last week and found some slickenlines and slickensides in the rock at the Bumpass Trailhead Parking. I would have known what I was looking at had it not been for your great and informative video's. I was able to share this information with my grandsons. Thanks.
That is awesome!
ありがとうございます！
Wow! Slicken lines…nice!!
Super helpful for perspective shaping as always.
Wow, this takes some sort of road cut prize, lol. As your voice got excited near the beginning I was realizing that was a fault with the slickenlines. I got excited seeing all the different directions faults were going in such a small place. What a lot of dikes, too. I've only ever seen scenic shots of the dam area. I've never been near that area. that is really an interesting geology location. I wonder where all the ash that produced the tuff came from. For a slow day there was a lot of traffic still.
Very interesting. When you get slickenlines like that, can those be formed from a single event... fast movement along the fault, or does it need to be slower, small movements over a long period of time, like striations from a glacier?
The slickenlines are created quickly due to sudden fault movements.
Been there but never considered the geology. Thanks!!!
Just fascinating, Shawn! It is mind boggling to see the immensity of it all. I've always wondered what a fault looks like inside, and your explanation of the side movement was very interesting. What would the rock look like if the motion had been up and down? Do you have that posted somewhere that I could look it up?
Many thanks for this presentation! It was just long enough to keep us geology neophytes from overwhelm. You rock! 😄👍
Hi Shawn, new subscriber!! Love this series. You're teaching me to appreciate the geology along the roads in a more learned way
Welcome aboard! Thanks for the sub and enjoy the existing videos.
Thanks!
I just followed your footsteps on the road cut with Google Earth “Street view.” Pretty cool.
All of the views, none of the traffic!
Over on the Arizona side there is a walk to “Liberty Bell Arch” that involves some “cross country” travel across bare rock.
I found a really cool xenolith about the size of a bowling ball that appeared to be Paleozoic carbonate rock incorporated into the tuff. (It had pretty clear development of arid land type chemical weathering caused by rain-drop solution.
If any viewers of this video are in the Hoover Dam area, opportunity to view a huge variety of rock formations is not to be missed.
Awesome Geology Shawn!
Another good one! Keep it up!
Thanks Shawn.
Awesome, thanks
very cool! Love it
Great job!
You can support my educational videos by clicking on the "Thanks" button just above (right of Like button) or by going here: www.paypal.com/donate/?hosted_button_id=EWUSLG3GBS5W8
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On a spring break college field trip in 2002 we got lit up by homeland security at the railroad tunnel above the dam on the NV side. We had to sit while 1 student was escorted to the parking lot to bring the vans to some get us. We swear we didn't see the no trespassing sign
Thank you!
Another great Roadcut video!
Not sure if this has been answered before, but how does the construction process alter what we might see? Would any of the fractures and coloration be accentuated by road construction?
For this location, I don't think construction altered anything we observed
This was fascinating. Is this an example, in an analogous way, to what is going on in Iceland on the Rekyanes Peninsula except the tuff is extrusive?
i love these
I just watched your road cut video on Union Pass, AZ. Do you think the same eruption event that created the tuff here is the same that created the tuff at Union Pass, since they are generally in the same vicinity. Thank you for these videos, they are fascinating!
Pretty tough tuff.
those intrusion of magma are neat could those faults go down into the bottom of the canyon i wonder if the water pressure could move a fault?
LOL!!! KEEP OFF ROCKS sign.
Looking at the amount of offset of those intrusions, near the end of the video, I have to wonder when the dam will be destroyed by an earthquake? Or how many earthquakes will it take to destroy the dam? Enjoy your videos! 😀
Thats a lot of tuft. I wonder how far it spreads out, or how far the ash flow spread from the volcano when it happened. How long did it last? Was it just one event that produced that much ash? How long after did the next basaltic intrusion happen? I always come away with more questions. lol Nice road-cut reveal. ;-)
I wonder about the inferred dike or sill and if one would take a series of thin sections at progressive distances from the contact, might there be some mineralogic evidence of thermal metamorphism? I.e., mineralogic zones correlated with temperatures. Of course one would have to be a better mineralogist than me. Also I am wondering if the force of the intrusion my have contributed to the series of local displacements that gave rise to all the slickenlined surfaces, particularly given orientations of the lines appear to be in different directions?
Are you familiar with the Red Rock area west of Las Vegas? There is a place in the Cottonwood Valley where there is an amazing display of geologic history going from undersea shinarump layers to shallow water layers including petrified wood to the Aztec sandstones, all within a stone's throw.
th-cam.com/video/coYimeWvC9g/w-d-xo.html
th-cam.com/video/oLofGgKDh4I/w-d-xo.html
Hello again. The videos that you referenced above are of the Aztec Sandstone and the limestone overthrust. The area I'm referencing is the strata below the sandstone as it transitions from aquatic deposition (probably sub-sea) to shallow water (with petrified wood) then up to the dry land sand dune deposits. This is best seen in the Oak Creek area.
It appears that the lines also may have been made from machinery when they built the road or the bridge?
at 4:08, you say that the small crystals in the clast indicates that the magma cooled slowly. shouldn't that be "cooled quickly"?
I think you've mentioned before about structures being built around potentially unsafe sites. With the faulting right up against the dam, would this not be a concern? Or is it because they are so old and unlikely to cause a problem again? Thx
I’ve been through there so many times. It looks so tortured and explosive! Any dating of these events?
Tuffs are ~14 Ma
Hi Prof. 1 question about slicken surfaces: are they the result of a long and slow movement of the rocks or Do they appear suddenly during earthquakes?
Quick, sudden movements on faults.
Ive heard the term (horizontal fault) I thought that was the jump the shark interpretation of the century.....then you walked right under a 40° uphill fault. Dont know if youvsaw that usually nothing gets by you.
Im just wondering how motivated was that tuff !? I think i can i think i can
OMG, tuff has become normal word to me.
Great news. Welcome aboard.
Thank you Professor Shawn for another amazing road cut. I have a question for you, is this area still seismic active because of all the faults in this area of the dam?
I don't think most of the faults are active but I am not certain.
@@shawnwillsey thank you. Have a great day today.
According to "Roadside Geology of Nevada" the tuff is "Tuff of Hoover Dam" and the authors do mention the dike cutting across the tuff. They describe the dikee as being compose of olivine basalt and basaltic andesite. Nick Zentner video streamed his first Geology 101 class after the 2020 closure live . The rock lab was taught by someone else so is not included and the class is centered on Washington state geology. I think that the geology community thinks of Nick as more of a knowledgeable presenter than a geologist. He acknowledges that when he puts his educator role as his strongest attribute over any research role.
was there glaciation in that area of nevada?...
No. Way too low in elevation and latitude. Much too warm.
@@shawnwillsey
if glaciers reached Wheeler Peak New Mexico then why not the Las Vegas region?...
3:05. You say sedimentary, but I think you meant igneous? (Some might think volcanic rocks are sedimentary...)
No I meant sedimentary in this case.
Pretty sure he was talking about the tuff - that's sedimentary, stuff that accumulates by layers over time that isn't hot to the point of being liquid/flowing. Yes, there were volcanic rocks, but the tuff was the sedimentary rock he was referring to :) As he said, all three types of rock can be found in the Hoover Dam area. This was a great example of two of them right next to each other.
@@imbwildrd3693 Thanks for the clarification, that would have been ambiguous distinction to me also.
If anyone could detail the nuance, how is a Pyroclastic flow defined then if it is distinct at all? Or is that possibly a spectrum of both and maybe defined in context? Possibly it is just a form of ash or tuff?
Tuff is a volcanic rock composed primarily of ash. In the video, I mention that the rock has the appearance of a sedimentary rock due to the clasts (rock fragments) when it is actually an igneous (volcanic) rock.
Where's the volcano, or other source of magma that ejected this tuft?
Not sure. That's the beauty of Random Roadcuts: going in with little to no knowledge of the location. I'd have to dig through references.
@@shawnwillsey Thank you for your reply. If you've identified tuft, or welded tuft, or whatever those rocks are, and they originated as volcanic ash, or by some other process of magma extrusion, or by whatever means that we categorize as "igneous," there is likely to be a history of volcanism in the vicinity. Can the source of the tuft be located, or has it eroded away?
Given all the evident faulting, how did the civil engineers decide this was a reliable site to build a high head dam? History has shown they made a good if risky choice.
Isn't is dangerous to build a hugs dam where there are so many faults?
looking for 'GOLD" down river Search light a few gold mines. Gold flows faults filling foot wall and hanging wall??? thank you ALL stay safe
Are the faults the result of an intrusive dike breaking apart a welded tuff?
No, the faults are younger than both.