Mystery of the Megablocks: how did these huge rocks move before sculpting by the Bonneville flood?

Team up with geology professor Shawn Willsey for some investigative geology. Along the Snake River, at Auger Falls park, lie huge chunks of basalt (informally called megablocks) that show evidence of movement and sandblasting by the Bonneville Flood, a colossal deluge (or megaflood) from 17,400 years ago. Help Willsey unlock the mystery of these enormous rock fragments.
GPS location: 42.62549, -114.51877
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Shawn Willsey
College of Southern Idaho
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Twin Falls, ID 83303

[@StereoSpace]

Your megablock theory sounds plausible to me. It certainly explains everything we see, and that's always a good start. LOL

[@jagers4xford471]

Maybe these mega block were under cut in place by turbulent water then fell into the pothole excavated by the water. This would kind of explain their near vatical orientation. Not knowing what the other blocks orientation looks like, my hypothesis may be a total moon shot. Love your videos..

[@shawnwillsey]

Thanks for your thoughts and kind words. So many mysteries to solve.

[@bagoquarks]

If the mega blocks were too large to be moved by the flood once pried off the wall and then toppled onto the floor, one can imagine the potholes being scooped out by the eddies around said blocks, and then the blocks tipping into their own potholes. Are the strata inclines consistent among the mega blocks or akimbo? The mass of the individual mega blocks might hint at the upper limit of the flood speed.

[@ericfavre2301]

i'm not even a geologist and not even close to the US but i love these videos that tell the story of our planet !

[@AvanaVana]

Hey Shawn, I don’t know how I missed this before. I love all things Snake River Canyon and SRP in general. Here’s another hypothesis. First, because this section of the canyon is so wide and there are so many melon gravels, it seems natural to say that the energy of the flood at this point would have been lesser than at other points along the canyon. Therefore the idea that the flood itself undercut or pried mega blocks from the walls of the canyon, only in this spot, and nowhere else nearby (and as I understand it, these mega blocks are fairly unique and there aren’t really other similar examples elsewhere), nor in narrow spots of the canyon or along bends where it the energy would be higher and undercutting more likely, seems to be ruled out. An alternative hypothesis is: before the flood, this was the location of a rather tall, impressive waterfall on the Snake River channel, perhaps larger than today’s Shoshone Falls, Pillar Falls, etc, and less chaotic since it would have been formed by normal fluvial processes and not an ice age mega flood, perhaps having more of a “Niagara” type of straight-ish edged escarpment, which was constantly being headcut upstream. Like many waterfalls, including Niagara Falls, the process of headward erosion undercuts the layer that the river channel falls over, causing massive blocks to fall off of the face of the waterfall and pile up in front of it. In a normal river system with such a a waterfall, this happens all the time, and the massive blocks gradually get eroded and carried away at approximately the same rate as the waterfall is cut headward upstream. However, something special happened here: the Bonneville Flood. The flood would have rapidly eroded this waterfall in the upstream direction, leaving the mega blocks which fell off naturally stranded in front of it, at such steep angles, while the valley cut headward during the flood, a mile upstream of here being the point where the Eden channel rejoined the main SR channel, creating some extra turbulence and destruction just upstream. It seems that maybe it isn’t a coincidence that just upstream of these mega blocks happen to be three prominent waterfalls in close succession, Pillar, Shoshone, and Twin falls. What if before the flood, it was more like one large waterfall where the mega blocks are today, or maybe a couple tiers in quick succession in that location, and the mega blocks are pieces of the waterfall’s face that were undercut by the paleo waterfall, and stranded there when the Bonneville flood quickly ate away the face upstream, flattening one very large waterfall out into three pretty large waterfalls separated by a few miles each, leaving the megablocks tilted, polished, and half-buried by flood sediments. It just seems odd to me that if these mega blocks came from the walls of the canyon, they wouldn’t be found all along the canyon, instead of concentrated in one place, and it seems weird as well that they are found in the slack water area after the Eden channel rejoinder rather than the Eden channel itself. It’s also weird that the megablocks aren’t closer to the canyon walls on either side, if they fell from the walls, especially since the current would be strongest in the center. It also seems like it’s not a coincidence that it occurs right before this succession of waterfalls. Mega blocks like this are commonly created when the face of a very impressive waterfall is undercut by its channel, but rarely survive along the channel as it eroded headward, but in this case the flood itself may have allowed the blocks to survive, by leaving them stranded and separated from the waterfall as the flood quickly cut headward… Edit: another hypothesis, possibly could work with the one above too. Some scientists believe there was stable outflow of lake Bonneville for 1000s of years prior to the flood, and that the catastrophic flood was the result of a massive EQ on the Wasatch Fault. It’s possible such an EQ could cause massive blocks to fail on the SR canyon as well. Now, as for why they wouldn’t all be located along the edges of the canyons, instead of in the middle, clustered in a single spot, perhaps such an EQ broke off large pieces of an already undercut paleo waterfall on the SR channel, and the flood continued to erode headward, creating today’s three separate upstream successor falls.

[@karlgant8953]

I like your idea of the mega waterfall created before the "flood" leaving big blocks more in the central area of channel during the "flood" and not similarly scattered along the edges up and down the channel. Makes sense.

[@toughenupfluffy7294]

I normally don't read long posts like this, but when Avana Vana speaks, I listen. Excellent hypothesis. I wonder if the stream competency has been computed using the size and weight of the melon gravels?

[@balesjo]

On seeing these blocks, my first thought was that the blocks were the result of slabs of basalt that fell from the cliffs during the Bonneville Flood, which would account for the rounded surfaces and the dip the blocks display. Beautiful area, love the waterfall.

[@hunt4redoctober628]

Lots of theories in the comments section but I would start with the basics first; check out the lithology and minerology of the megablocks to determine if there is any correlation between these and the lithology and mineralogy of the rock layers forming the canyon walls. That would then help to either eliminate or reinforce the theory around possible pillow lavas happening during a large flooding event. At least then you will know for sure the origins of these blocks and if they have been deposited through mechanical means or not. Just an idea..

[@charliewatts6895]

Yeah, that's where my mind was going on this. Might be a PhD paper in there for a student of geology.

[@JanetClancey]

That’s exactly what I thought… deep undercutting and huge block falling off thanks Shawn

[@gerrycoleman7290]

Initially I was wondering if they are flood eroded remnants of fissure flows. I would want to investigate to see if they are bedrock controlled or deposited on the surface. I do like your idea as a possibility.

[@Yetibiker67]

Thank you Shawn! Another great post. Keep up the good work!!

[@briane173]

Your hypothesis is as good as any, quite honestly. Makes sense; it's not like the outcrop you're standing on is isolated; there are several of them all down the canyon. The variety of orientations speak to these structures falling straight down off the cliffs after getting undercut by fast-flowing water and essentially landing in the orientation they now sit in and they are just getting pummeled with this ridiculous amount of water, helping to erode away whichever side was facing the onslaught when these formations finally landed on the bottom.

[@user-lf1sd6bo5x]

Quite interesting formation. We have an area in Oklahoma called the Arbuckle Mountains that are also formed from vertical rock that seems to have been layered on their sides.

[@bobbyadkins885]

I believe you’re on point with your explanation, kinda had me confused at the beginning calling it an outcrop, I always associated that term with bedrock formations, not detached boulder blocks. Love your channel, just found it recently

[@clousetechworkshop7597]

I think you are right that they dropped from the cliffs, I think the flood composition when they dropped was likely very heavy with silt and debris and the blocks were semi-rafted into the channel and dropped relatively gently into place as they sunk through the thick debris-flow-like flood. If they were moved by fast flowing un-choked water I think they would have tumbled more and broken apart, blocks that size especially of already semi-fractured basalt likely wouldn't survive much tumbling, unless they are part of a super huge break of from the cliffs and they themselves are left overs of a larger chunk breaking up.

[@kenbrummage4429]

Hi Professor! I love the videos, welcome to the PNW. I believe those rounded structures in the basalt are pillows. At 5:35 you can see a gorgeous bedding plane that separated different flows. I would interpret the one on the left was deposited under water, the flow on the right was deposited sub-aerially. There is a great shot of them at 4:30 where you can see what appear to be pillows in shape that have conformed to the other pillows around them. This is typical in the Columbia river flood basalts, though I'm not sure if they made it to your location. If the Bonneville Flood was anything compared to the series of Missoula megafloods I wouldn't be surprised at all if these megablocks were moved by one or many megaflood events. (The ripple marks left in the west bank of the Columbia River by Wenatchee is one of my favorite pieces of evidence that points to the sheer scale of these floods.

[@shawnwillsey]

Hi there and glad you are enjoying these. These basalts are most definitely not pillows. They do not have the glassy rinds, palagonite, and other features. There are a few limited outcrops of pillow basalts in the canyon but not here. I have two videos of these you can check out if you want. kzbin.info/www/bejne/fWeom4iadpKDbbc and kzbin.info/www/bejne/j4PWYoiMh896j5I I think the large polygon shapes you see at 4:30 are the tops of large, somewhat crude columnar joints. These basalts are not Columbia River flood basalts and much younger (2 million years to 95,000 years). Unlike the Missoula floods, the Bonneville flood was a singular event that lasted weeks to months. As an aside, I will be in Wenatchee at the end of the month for a field conference so please send along any must see geology or good locations for videos. Thanks.

[@kenbrummage4429]

​@@shawnwillsey Hi Professor! I spent some considerable time writing up an email with my recommendations for must see geology a while ago - I hope you've had the chance to read that. In addition, if you're near UW campus, I'd love to show you the geology dept. and our rock garden. kbrumm

[@shawnwillsey]

@@kenbrummage4429 Hi Ken. So sorry I haven't got back to you yet. I was on a week long Salmon River trip and then went straight to Wenatchee for a field conference. I wanted to take the time to send you a proper reply but haven't had the time yet. I won't be able to get to UW on this trip as I need to head back to Twin on Sunday. Your recommendations are great. Not sure how much I will have time to see sites because it is so blazing hot here right now. Today was about 108F. Yikes!

[@davesouza610]

Megablocks have a pillow appearance from certain angles. Without knowing the strata of the valley floor, could it be they were actually basalt dikes/fractures that erupted whilst submerged under the Bonneville flood? Or, created at an earlier time, then covered in tufts that the floods eroded away?

[@shawnwillsey]

They definitely are not pillow lavas or dikes. Based on their layering and orientation, the blocks have clearly moved a bit.

[@sscoxsscox]

Hey Shawn, love your channel. Since IMMG has not been doing field trips last few years, it's like virtual trips. If you recall our discussion when you led a trip for us into this area a few years ago, we came to the same conclusion. The "megas" are too big to have been transported but certainly were eroded/polished and re-oriented by flow after they were deposited. Couple of possible mechanisms that brought them down: undercutting in an early phase of the flood, or maybe vibrational shock as the overland and channel flows merged. We can not imagine the forces involved!

[@shawnwillsey]

Hi Steve. Hope you are well. Yeah, your IMMG folks might like my videos as a way to get out in the field in a virtual way.

[@macking104]

have you watched Nick Zentner’s Washington geology field trip videos?

[@sscoxsscox]

@@macking104 Yes.

[@maxisp1000]

Unimaginable flooding and power.

[@MsMsmak]

I have no ideas but boy oh boy that is very interesting to think about!

[@jamessmelcer616]

Thank you Shawn, another great show. Keep up the good work. I appreciate you sharing your expertise. Jim

[@dougbotimer8005]

Climbed all over “megablocks” as a kid without giving it much thought. Of course, I’ve learned much about this area recently from you. My notions of the Magic Valley topography and geology have, until now, been based on volcanic activity building up and erosion cutting the canyons and other features. With that in mind, I would tell myself these outcrops are the remnants of volcanic dikes, and being harder than the material they fed through remain after the flood eroded the material around them. But, I’m no geologist.

[@sergiovelazquez1259]

Thank you for sharing this video

[@stevew5212]

I agree on how they got there and why they are there. I did not know that the boulders down along the Snake at Hermiston and Swan falls were all from the great flood.

[@tristangreaves2704]

Always enjoy your videos! Especially the local stuff like this, the mega blocks and melon gravel sure do make for some fun mountain biking and rock climbing!

[@shawnwillsey]

Hey Tristan. Thanks for watching and learning with me. Hope you are well.

[@tolson57]

I agree with your conclusion. Someday you can send grad students out to map the layers and their thicknesses and try and match them to the current canyon walls.

[@marklang5169]

Fun vid thank you.

[@BruceJividen]

There are some giant blocks like that in the Ephrata fan coming out of Grand Coulee.

[@paulhopson7652]

Hey thank you for taking time to make these videos. It has been a treat to view the geology of other states and to hear how different formations have been created. My thought on the question is that these formations are resulting from how the two channels of the Bonneville flood meet into the larger flow. I imagine it would create a short of a Y shape and that the inner side of the Y so to speak gets wore down rather quickly creating a sort of standing rock formations. These then get undercut by one force or another, likely by the water as the Y zips itself further upstream following the erosion and then plop over. I suppose a way to validate or check that hypothesis is to check the sizes of the formations moving upstream and if the pieces get larger then this may have some truth to it.

[@KozmykJ]

My first question was "Are the ages of the block basalt and the canyon wall basalt coeval ?" But from reading down, I'm inferring that they are.

[@yavva7015]

With blocks being intact and the flood going on, they couldn't have moved far from where they landed, or they would have broken up more into normal melon gravel. Also I would guess that they fell later in the flood or the water would have been strong enough to seperate them that way, too. My guess would be that there was an island in the flood path that failed later in the flood.

[@PukinBigBird]

Shawn, Great video and well presented. My take is similar to others here except the time issue. At the early stages of the flood, the snake river canyon was not as deep and the river would have found alternate channels to pass the flood waters. This would have left numerous channels being cut leaving many small islands type structures that would then be subject to catastrophic erosion as the river picked up energy until the islands would be pounded by the boulders being released by the walls of the canyon. These islands were then cut down by the passing boulders until the tops then collapsed as we see them today. I think that the structures in the centennial state park show what these structures would have looked like in the earlier stages of the erosion. I would love to see a video on your take on the formation of the Rocky Mountains.

[@LouinVB]

They are the remnants of Bluffs that existed prior to the flood. The erosion by water is evident as you point out. During the flood the Bluffs are undercut and they toppled over in place.

[@davec9244]

sound good to me thank you

[@philbox4566]

I suggest that these mega blocks were undercut in place and gradually their elevation was lowered from successive floods.

[@williamnicholson8133]

Rocks in ice would flow quite easily during a torrental flood.

[@leechild4655]

Before you said how you think the mega blocks got there I thought the same thing. Big sections of wall either fell or were moved from earthquake and lava to there spots where they have sat and weathered?

[@leechild4655]

Also, the distance of these outcrops to the mountain side of today must have grown aswell from erosion. the mountain, rather lava walls from which these fell where much higher and closer to where these pieces lay now.

[@mariejanes7207]

Great channel, just found it. I tend to agree with the opinions stated about y-zippering back from the point of merge, and/or that the blocks originated in the valley center (akin to steamboat rock). You mentioned the tremendous turbulence at the point of the flow merge. The side canyon walls are undercut. It seems likely that an undercut could happen in that valley center, particularly with the turbulence, allowing source material at the center to be freed to roll to angled positions (and then be pummeled by the basalt boulders and other debris). I didn’t look up google earth but it would be super interesting to see if the complex of megablocks has a higher order ripple pattern. So essentially- I think it’s too far, for those megablocks to have traversed from the sidewalls; I think they were sourced in place with foundations undercut allowing them to be tipped to the current positions. Thanks for the fantastic videos, will add you to my binge geology queue!

[@fredwood1490]

If you are allowed to dig, it might be useful to cut into the mound the block is sitting on, to see how far down it goes and what is under it. The up stream face of the block is almost polished flat so I assume that was done by the flood.

[@mickie7873]

As you, yourself indicated "if you know about magma", I'd say that these outcrops of huge boulders (islands) were originally formed by fissues, (your're saying that they are basaltic). They also showed the air bubbles, so this was active magma. The magma was cooled and broken into fractures by the cold water and their edges were rounded. Many huge "water events" have occured in the development of the Earth's land masses. I say the same about your "mellonball" video. Lots of massive water events....water, in and out over a long period of time. Earth's development is a puzzle as we know, but it sure is enjoyable conjecturing. (thats my "two cents" interpretation.)

[@stereomonologue]

Hi Shawn! Another great video, very intriguing. So I am just curious about the large boulders you mention at around 1:07 - you say these were transported by the Bonneville flood and rounded through banging into each other (eroded I guess) etc. So in terms of time how long does this process take, approximately? Feels like must take quite some time to shape and round off those big boulders, or is perhaps the material pretty easily eroded?

[@shawnwillsey]

Not sure it can be easily quantified but in this case, very rapidly. The boulders were plucked from the canyon wall and tumbled downstream, colliding with other boulders. The more frequent and energetic the collisions, the quicker they become rounded.

[@davidk7324]

I think your hypothesis is plausible, Shawn. As someone mentioned below, the canyon walls would have been closer to the resting place of these rock fragments before 14,500 years of erosion/collapse of the rims. Just an average of 0-1" on average/year would add up.

[@johnbollenbacher6715]

The problem I have with it is it seems like a lot of rounding to be caused by a single flood event. But maybe they were already eroded by the river.

[@Kalebshadeslayer]

Your idea seems on point to me. Perhaps the large rockfall event was caused by undercutting of the cliff face, Allowing these large singular chunks to eventually fall as that ledge collapsed.

[@ped832]

Along the Blackfoot river is similar but on a smaller scale.

[@JonJaeden]

Is the polishing on all the different megablocks oriented upstream? Is there any reason to question if the megablocks could have "rolled" as far as they appear from the cliffs? It would seem the same water that cushioned their fall and prevented them being shattered into small pieces would also exert drag on their lateral movement once they fell. Or could the original cliff face have been eroded to the distance we see today? Just found your channel tonite and really enjoying it.

[@PopsMdub]

Hmmm, interesting puzzle. Could it be that they were never part of the river wall cliffs at all, rather they were simply larger pieces already buried there in place that became islands, submerged or otherwise, during the flood, and erosion just simply carved them out of the surrounding material. Perhaps some of the other boulders that are strewn about were once part of these mega blocks. I found it interesting and puzzling also that at about 8:45 in the video you point out the pahoehoe still beautifully preserved on an area of the mega block. Now my question about that would be, how did this stay so well preserved and defined while much of the rest of the surfaces appear to be very eroded and worn by the water and debris flow? If water and debris flowed over it for long wouldn't that feature just become indistinguishable? Anyway, great stuff as always. Be careful out there and keep these coming as often as you can. Thank you.

[@kirklaird8345]

At some time in the past the valley was filled with basalt. The basalt eroded away over time. Seems to me it is quite possible that the mega-blocks are simply the remnant of the basalts filling the valley, undermined by river erosion and scoured by the Bonneville floods. Something like Steamboat Rock in the Grand Coulee which is an island remnant of basalt flows that will continue to erode mostly in place.

[@shawnwillsey]

The orientation of the basalt in the megablocks doesn't jive with your idea. Basalt oucrops in the valley should show volcanic layering and stacking of flows that are subhorizontal, similar to what is observed on the canyon walls. Instread, flow features and layering in the megablocks are steeply tilted, about 45-70 degrees with respect to horizontal, indicating they were transported and moved. They have been moved and are not in place (like Steamboat Rock).

[@kirklaird8345]

@@shawnwillsey Sorry I wasn't clear. My suggestion is that at one time these rocks were like Steamboat Rock but then subsequently undermined and toppled over - staying pretty close to their point of origin.

[@charonsiouxsie949]

Maybe this is an example of the lava incorporating with a flood. Pahoihoi meets flood waters?

[@jeremiasrobinson]

Is there a part 2 of this with your updated conclusions?

[@MrColinManning]

That's what I was thinking.... That the megablocks are chuck of the basalt cliffs that moved during the flood. Perhaps the basalts can me matched to areas stil sitting high on the cliffs?

[@DayRider76]

Yea, looks like the roof came down. Or a full strata feature that got wiped out.

[@agrifoguy]

The edge of a waterfall that was undermined by the Bonneville flood and deposited in the river.

[@lauram9478]

❤❤

[@lauram9478]

❤

[@EtnoZam]

< Eric von Daningan has joined the discussian >

[@3xHermes]

👍

[@wadelangley2263]

Full of gas bubbles , could that make them more buoyant ?

[@bulwynkl]

Any reason why they couldn't be in situ? i.e. the walls of the canyon where where you are when erosion - presumably from massive flood events - undercut the cliffs and they fell off? then continual flooding or subsequent flooding moved the cliff faces further away? No need for much lateral movement then.

[@shawnwillsey]

These large boulders are clearly not in place based on the orientation of lava features such as flow surfaces, vesicles at top of flow, etc. They should be nearly horizontal but instead are dipping 45-70 degrees.

[@stevemackelprang8472]

Is there a way to date the lava? or more likely, chemical analysis... are these blocks from the same eruptions as seen along the rims of the canyon... ?

[@shawnwillsey]

Isotopic dating of rocks is pricey as is a full geochemical analysis. Without that data it would be very difficult to determine the block's origin.

[@BretBerger]

could the megablock's rafting have been enhanced by contact with clay beneath, possible in conjunction with pulses of flooding and movement and deposition of clays.

[@shawnwillsey]

There is no clay beneath. The valley floor is lined with basalt and rhyolite (just upstream).

[@mcc94549]

Hell, Look at the orientations of the other blocks- How random are they? Can they be large blocks, ripped up from the local bottom, only slightly (?) moved by the flood water- rolled short distances. Obviously the rounded areas were smoothed by the flood water, but the blocks themselves may only need to have moved enough to create that near-vertical tilting. This mechanism should have led to fairly random orientations between the blocks. It looks to me that the blocks are quite a distance from the vertical sides of the channel- probably too far for the blocks to be (relatively) intact landslide blocks.- although consistent orientations of the blocks could falsify my idea (its not even a hypothesis at this stage, of course).

[@shawnwillsey]

They can't be from below, because rhyolite and much older and different basalt underlies this section of the canyon. I will work on measuring the orientation of the basalt in other blocks but they are not consistent. Check the area out on Google Earth if you get a chance. The size and clustering of these blocks is impressive.

[@churlburt8485]

they could have been undercut while the canyon wall was much closer.

[@Wvanbramer]

No chance of finding an origin point along the canyon wall for these megablocks?

[@johnbatson8779]

is there any evidence for localized seismic activity that could have created instability and release of these large blocks of basalt to tumble down to their current position before the Bonneville Flood washed the melon gravels down?

[@markcollins3418]

Hey Shawn. If you and Derek Bristol got together, you could do something epic. Maybe you already have. Kinda cross-discipline, but it could be epic.

[@shawnwillsey]

I had to look this guy up. Big caver, eh? With my climbing background, we can both handle ourselves on ropes. Caves have great geology features.

[@markcollins3418]

@@shawnwillsey "Leave no cave unextended" ...Derek Bristol

[@daleolson3506]

How many pounds is 3or 4 meters?

[@GunsandCoasters]

I have no geology skills with which to make an educated guess. 👽? 😃 It's just a subject that my brain has decided is interesting. I just noticed that early in the video you gave a size in meters, then went back to feet. I think that's the first time I've heard you use metric (and I've watched all but a few of your videos). I figured that would be pretty standard, and thought it was odd that you used imperial units.

[@shawnwillsey]

As a scientist, metric is my standard but I know most viewers would rather hear feet so I try to use that more. Sometimes I slip back to metric as you noticed.

[@TheKrisg50]

If the blocks fell off the sides of the canyon and are to big to be moved by the flow of the flood, how did they get into the middle of the canyon?

[@shawnwillsey]

During the flood, the entire canyon was filled with water. Undercutting of the canyon walls by the flood led to instability wherein a section of the canyon wall failed and slid into the floodwaters. The buoyancy of the water and the velocity of the flood allowed the blocks to move farther from the cliff face than they would otherwise. Also, the canyon itself may have been narrower as the flood commenced and erosion widened the canyon.

[@TheKrisg50]

@@shawnwillsey ok. That makes sense. It must have been something to see…..

[@WayneTheSeine]

@@shawnwillsey The canyon being far more narrow at the time fo the flood was kinda my take as well. This would also tremendouosly increase the flow and power of the water or slurry as well. I can imagine the initial flood water being an extremely thick slurry of mud and stone which could support massive loads and also blast away a lot of the canyon wall. The shear brute force would be almost incomprehendable. Have any core samples been taken that would indicate how much deposition occured in the valley floor? This would give some indication of just how much of these blocks are hidden. God knows how big they actually are.

[@Lorwildrose]

Could there have been a small masa in the valley that the flood undercut and the blocks fell in as it collapsed?

[@shawnwillsey]

Possibly.

[@Lorwildrose]

@@shawnwillsey my idea comes from growing up in the Red Deer River Valley Alberta and seeing mega flood remanence but on a lot smaller scale.

[@mhansl]

Is there any evidence of scouring around the megablocks?

[@robertbowker7766]

Had you considered the aftermath of any glacial ice? As you know glacial ice can move massive amounts of material ahead of the eye structure especially if it's being driven by something like the Bonneville flood event.

[@shawnwillsey]

No glacial ice in Snake River Plain. We had a few small alpine glaciers in Albion Range (south of Burley) and in the central mountains to north, but no ice at these low elevations.

[@789563able]

Not much other choice, really. Too big to have moved very far, so they had to come from the canyon walls.

[@mcc94549]

Oops, I meant to say "Hello" !!

[@madsotzenandreasen7145]

my gues was basicly the same as yours.

[@scottchase8014]

Oh just petrify me and make me into stone grind me away some other day