Exceptional Eocene Dikes Intruding Idaho Batholith in Central Idaho

Visit some outstanding roadcuts of Eocene dikes along the Banks-Lowman road in central Idaho with geology professor Shawn Willsey. These impressive geologic features were the conduits that carried magma toward the surface about 45-50 million years ago.
00:00 intro, location
00:16 overview of Eocene dikes in roadcut
03:31 walk down road, South Fork Payette River
07:30 large dike, mine adit
09:20 Little Falls
10:00 outro
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Shawn Willsey
College of Southern Idaho
315 Falls Avenue
Twin Falls, ID 83303

[@mickie7873]

Thank your for taking the time to share this type of geology with us. Just super, seeing the dikes.

[@samtasticlatte]

Very fascinating. I love the story the land under our feet can tell us if we take the time. Thank you for stopping by there.

[@Riovientoselva]

What a beautiful dikes ! ! Y yo que estaba contento cuando encontré un diquesito en mi ciudad ! JaJaJa. Caminaría por horas mirando y clasificando rocas por esos bellos lugares ! Gracias por compartir Shawn !

[@sparkmadd_IZM]

Thanks for being safe...and sharing this amzing geology.

[@PlayNowWorkLater]

That Google Earth Pro is pretty slick.

[@shawnwillsey]

Leveling up very slowly.

[@mjleger4555]

I know that Planet Earth is a very active planet, but to see some of the evidence of her activity millions of years ago is mind-blowing! Thanks for the informative explanation of that contrasting light and dark rock, I had wondered about that!

[@grandparocky]

Shaun you are at one of my favorite rock collection sites! The rocks on the right are full of manganese dendrites.

[@Faelani38]

Thank you for showing these awesome formations. The area is very beautiful.

[@davidk7324]

I drove from Lowman to Banks yesterday--a trip I've made hundreds of times over the decades. Before the late 70s that road was a dirt washboard and narrower. An odd minor benefit to horrible fires is that sometimes the underlying geology is revealed. A couple burned areas on the Banks-Lowman road brought that to mind.

[@briane173]

Wow I'm just blown away by the starkness of these basalt dikes. Interesting you bring up crustal extension; one of the theories behind the Teanaway Formation in the Cascades is that the area appears to line up with an old divergent plate boundary between the Kula and Farallon plates, which provided a tear in the slab to accommodate slab rollback. The difference in how those dikes formed was that the cracks in the existing rocks were formed not by extension but by _compression._ It relates tangentially to Basin & Range extension, but only to the extent that the Sierra block was pushing into the Oregon block which was - and is - squishing Washington between the OR block and the Canadian Butrress. That had the effect of opening up cracks like how you open up one of those plastic coin purses - those ones with the slit through the top so you squeeze it and it opens the hole to put coins in. That's essentially the morphology that was taking place to open up these cracks in the existing rocks, and the magma rising through a slab window took advantage of these 6 dozen or so coin purse slits and intruded basalt through them.

[@fallinginthed33p]

I think Nick Zentner brought up something similar to explain magmatic activity in Idaho. A subducting plate that used to be a spreading center unzipped at depth, something that had to do with the Siletzia continent.

[@patmayer7222]

Land o' lakes,wi...here,for class......great intro with location,,cool...tnx,,,pat&family............knowledge = power.

[@sandrine.t]

Oh wow!! These dikes are truly amazing! Thanks for sharing, Shawn. I love your videos, they really make us feel like we're there with you :)

[@jerryofsanfrancisco]

Always a pleasure to see your videos. (for many years I had a cough & did not realize that I was allergic to fragrance, cologne, shaving creams. Once I eliminated fragrance my coughs stopped!).

[@lonthrall5613]

Thanks for taking the time to post this!

[@burpleson]

Very interesting , as always. Thanks.

[@dianespears6057]

Enjoyed the impromptu view. Thank you.

[@catztail64]

I really enjoy your videos. They are very interesting and informative and you make it easy to understand. I have decided to take a class from you in the fall of 2024 and am really looking forward to it.

[@shawnwillsey]

Wonderful!

[@LisaBelleBC]

Fascinating! Thank you!

[@shawnwillsey]

You can support my field 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

[@treborupp]

Nice. Thanks for sharing

[@briane173]

1:44 That dike is a SPECTACLE! I've never seen such a stark contrast between the dike and the rocks around it. The Teanaway formation has a treasure trove of basalt dikes but you almost have to get right up on them to ID them as dikes. _This_ one is a no-brainer -- as well-defined as they get!

[@KozmykJ]

A striking contrast there.

[@craighoover1495]

Thank you again. I am very sure I have been over this road in the past (>30 Yr) and I probably looked at these without seeing them. I am glad you saw them and showed us.

[@muzikhed]

Impressive setting.

[@stevewhalen6973]

Thanks!

[@oddevents8395]

F'n cool Professor!

[@marydd4147]

Beautiful area!! Love knowing the geology! We moved to south central Oregon - occasionally we find small pieces of petrified wood - but we (we're not geologists) think our property was mostly a lahar due to the chaotic mixture of huge boulders, rocks and dirt and very few non volcanic rocks (rarely we find some calcite, some type of what looks to be agate, and petrified wood - some look vitirifed). Although we're amateurs we do love knowing geology. Thank you.

[@shawnwillsey]

Very cool!

[@inyobill]

09:33: I'm a bit surprised that you didn't point out that the small fall was a result of less resistant material being eroded on the down stream side of the dike crossing the stream bed. Or maybe it was an obvious point? Very interesting presentation, as always. I was able to point out some relative dating techniques to young folk I was hiking with in the High Sierra. Had a nice exposure of several intrusion events into the granitic host rock, easy to trace the sequence of the at least three events.

[@davidsims4396]

Thanks for makingn this video

[@shawnwillsey]

It's my pleasure

[@billhollinshead7843]

Molybdenite and graphite look similar, even though molybdenite is a bluer silvery gray than graphite. One easy way to distinguish between them is their steak color on glazed (as opposed to unglazed) porcelain. Graphite leaves a grey streak while molybdenite leaves a green streak. That glazed streak color is also a mnemonic for Molybdenite’s chemical formula MoS2, or MoSS green.

[@rogercotman1314]

Loved this video. Thanks for the continued igneous dike education. Thanks Shawn .................. 63 like ..............

[@williamlloyd3769]

One wonders at how much pressure it took to force the basalt through a fracture and create a dike?

[@JanetClancey]

Wow!!!

[@merryhunt9153]

It's hard to think of earth processes that cause extension of rocks. Doming and anticline formation, maybe. Maybe something strange going on with the Farallon Plate. How about this? The granite of the batholith formed joints. When the basaltic magma started coming up (for whatever reason), it found its way into the joints and shoved the blocks of granite apart. It wouldn't be extension allowing intrusion, it would be intrusion causing displacement. Maybe the granite was still deeply buried, not really solid yet, and was surrounded by hot material which yielded when the granite mass got bigger. Thanks for a great video.

[@OdinsChosen208]

dang the south fork has some water still this late in the season

[@grandparocky]

That is the Moly 8 mine!

[@philsigman9088]

Shawn, have you ever went up to Bear Valley, about 20-30 miles above Lowman? There's a place up there with several giant house size boulder formations that have become more exposed by a recent forest fire. These things are gigantic and the road runs through the area with boulders on both sides.

[@shawnwillsey]

I have not been here. Send me GPS coordinates if you can.

[@philsigman9088]

@@shawnwillsey I tried to find the place on Google Earth with no success, yet. The area has no cell service either.

[@grandparocky]

One of the largest deposits in the U S of Molybdenites!

[@lauram9478]

❤

[@chucklearnslithics3751]

I imagine the plumbing under Yellowstone currently looks something like this, just a little warmer and a little more fluid. Is that a fair visual?

[@paulcarney8157]

Maybe the falling river rapids indicate erosion resistance due to dike crossing river bed?

[@101rotarypower]

Hey Shawn, Possible you could do a segment on the "Geometry" of how dikes are formed please? Always curious are dikes filling voids from extension, melting existing material, or spreading existing material under pressure. Where is the material the dike replaced? Probably many different ways/combinations, but never see anyone try to convey the diagnostic clues to visualize what happened when intruded. It would also be nice to speculate on the depth, temperature, melting point differences of the base material dikes are intruding. Sort of like how you can see vesicle bubbles so probably closer to the surface when formed, so does that mean the granite was completely solidified when intruded and probably "cool" ? Why is there such a sharp contact, what physical reasons causes that? Maybe even a rough time scale of intrusion and solidification? Those thin long dikes that come to a very sharp point are confusing, knowing we only see a 2D slice, it would be great to get a better dimensional understanding if you are able to convey that information how to understand how they are likely formed? Thanks! Really enjoy your on location POI!

[@shawnwillsey]

Usually dikes fill existing fractures (or weak zones) in rocks. They do not melt the existing material although you may get some contact metamorphism or other changes to wall rocks along contact with dike. All your questions are really good and I hope I can address them at some point. If you haven't already, here are a few other dike videos I've made that might help a bit. Feeder Dike in Iceland: kzbin.info/www/bejne/Z6emhoWEiL-ih5o Sawtooth dike: kzbin.info/www/bejne/fZnXqouYYtecb6c

[@zviperco]

Hello Mr. Willsey! How can you tell the difference when a dike rises vertically through cracks in existing rocks from layers of rock that were once horizontal and later pushed into their current position due to tectonic forces?

[@shawnwillsey]

Good question. A dike was once magma so it will become an igneous rock (made of crystals). You may also see discoloration along wall rock as the magma "baked" the existing rocks. The dike will also cut across the existing rocks (that's part of its definition). Rocks that were once horizontal and then were titled to vertical or some other orientation are likely sedimentary rocks made of grains of sediment or organic material. All the rocks that existed at the time of the tilting will get tilted. Hope this helps.

[@insAneTunA]

👍

[@leechild4655]

Those dikes could be called erroded and exposed lava tubes but, dikes is easier to say I guess. The geologic features of the continental u.s. is fascinating because of so much erosion that exposes so much of the deep past. It looks all beautiful to everyone but geolocically its like a vast wasteland of rock sand and water. Still, looks beautiful.

[@rogercotman1314]

Interesting, the use of lava tubes and magma dikes together.

[@briane173]

@@rogercotman1314 Lava tubes are tubes though -- they're hollow. The dikes are filled with basalt with no space between them and the rocks on either side.

[@rogercotman1314]

@@briane173 Correct, the statement from the other person, I found interesting ......................

[@tompowers8495]

👍🤔🌋

[@JPREEDY77]

Ok, @0:23 that looks SOOO much like the dikes going up the Salmon from Riggins. Hmm, have these been associated in any way with CRB? As my macro brain zooms out, it is very difficult not to see this as injected banding spread from the CRB and associated flows. Sorry, autism imagination happening as we speak, ultimately, reconsolidated the banding ends up looking the same as in Gneiss. Of course we are several million years downhill from that so seeing the entire in situ bed is nearly a terminal illness. But fun!

[@shawnwillsey]

Similar rock type (basalt) but very different ages. These dikes are Eocene (~45-50 Ma). CRB is about 17 Ma. Also there is some difference spatially. No CRB basalts are this far east.