This is geology B with all of us trampled.
Many hundreds of films have been shot on location in the American
West. The rugged inhospitable
Landscapes are an integral part of what gives so many American
westerns their distinctive character.
Although the region is vast stretching from the Rockies in
Wyoming and Colorado to Utah. New Mexico, Nevada, Arizona, and
California, a few locations have captured, the Lion's Share of
the film industry's attention What is it about these
Landscapes that makes them so photogenic and how do they get
that way? In this episode, Craig Jones
cast light on the answers to these questions.
He is a professor in the department of geological
Sciences at Colorado University at Boulder, his research aims to
uncover the origin of mountains and elevated topography and
continents primarily in the Western United States.
His main tool for doing this is seismology, but he also
incorporates observations from other disciplines such as
gravity measurements palette. Ultimate tree and petrology.
He's written a book on the Sierra, Nevada and leads field
trips to the rugged terrains. We're discussing here.
Craig Jones, welcome to geology B.
Thank you very much for having me before we start talking about
the specific locations that became Hollywood favorites.
How should we approach the question of understanding how
the Salient features of today's landscape came?
To be the simplest way to think of it is in three parts.
One is basically the intrinsic characteristics of the Rocks
themselves. So how they're actually
constructed what materials were used.
Then the physical and chemical processes that then affect the
Rocks after their created typically we're talking about
erosional characteristics and then to view these kind of
Landscapes, the present-day climate is an important
component to be able to understand why we get these kind
of Landscapes. Okay, we're going to focus on
just two very distinct areas. In the American West that have
been the favorite of film directors, the Colorado Plateau,
which covers parts of Colorado, Utah.
New Mexico, and Arizona, and the Alabama Hills which live, 50
kilometers, west of Death Valley in the Sierra, Nevada.
Let's start with the Colorado Plateau, concentrating on
Monument Valley, where over 60 major films were shot, starting
with Stagecoach in 1939 and including the classic, John Ford
movies with John. Wayne will also touch on a few
other locations in the Colorado Plateau.
Such as the Grand. Canyon Zion and Bryce Canyon.
What is the origin of the rocks in the Colorado Plateau?
The rocks that are present in. All of these places are
sedimentary rocks. Rocks are made up of what was
originally mud and sand. Or little limey creatures.
It's varied a little bit over the history of the Colorado
Plateau. Most of these deposits have been
made within about the last 500 million years.
One of the important characteristics of these
sedimentary rocks is the variation of them over time and
it's that combination of the variation of seas rising and
falling. Lying and mountains, rising and
falling that gives you the opportunity to have this diverse
arrangement of sedimentary rock, which is what leads to these
dramatic Landscapes. So, you mentioned shorelines.
So, do we know what the depositional context was for the
materials that make up these rocks?
Yes, it's varied quite a bit. So for instance, if you're at
the Grand Canyon and you stand on the rim of the Grand Canyon,
you're standing on the Kaibab Limestone, which is a marine
deposit but you go to Monument Valley.
Valley and you look at, wonderful spires that are there
and you're looking at the dish, a Sandstone, which is sand dunes
kind of like what you would have now in the Sahara.
And then there are fluvial deposits River deposits that
are, for instance, sitting in the organ rock formation sitting
at the base of those spires in Monument Valley.
So we've had quite a variation in a really is the fact that
it's come and gone with these different environments that
allows for all this diversity. Hmm.
Interesting. We have both Marine Fluval and
alien deposition in different places.
What sort of time scale? Are we talking about when this
deposition got going? And how long did it last?
Well, of course, it varies from place to place for instance, at
the Grand Canyon, most of what you're looking at the bottom is
the to Pete Sandstone, which is a little over 500 million years
old. And at the top that Kaibab
limestone is a little over 300 million years old.
So there you're talking about 200 million years of time.
Of course, there's a significant amount of that time.
No rocks were deposited at all you move over to Monument Valley
and you're looking at somewhat younger rocks which overlap in
part. The Kaibab Limestone but they
were closer to an ancestral rocky mountain range that
existed here in Colorado, Monument Valley to the West in
Utah and Arizona. So that time period was actually
so much shorter for everything. You see in Monument Valley,
probably maybe 50 million years. And then if you went to
something much younger, your talks about Bryce Canyon
National Park, the Rocks, there are pretty much deposited within
about 10 million years It's so different places are sampling,
different parts of the geologic history of the Colorado Plateau
and are representing different durations of time.
What was the larger tectonic context at the time was this
before or after the creation of Pangaea and did North America
already exist as a intact piece of continent at that time?
Well, North America was definitely at that point.
Before Pangaea assembled we call it laurentia because parts of
what her today, North America were at the time on other
continents. But this area in the
southwestern part of the United States was definitely part of
laurentia and part of North America.
Parts of that geology predate Pangaea.
So for instance, the section you see in the Grand Canyon for the
most part is older, the stuff. You see in Monument Valley was
accumulating pretty much. At the time that Pangaea was
finally being assembled. And so those answers to Rocky
Mountains, were a product in part of the final closure of an
ocean between South America and North America.
And then number of the rocks that are present are younger and
actually date to win. North America had separated once
again from pieces of Pangaea. So Zion National Park.
The big Sandstone Cliffs there, Bryce Canyon National Park, both
of those house. State Pangaea.
So, as you mentioned earlier, the depositional environments
are very different from place to place.
Some of them were Fluval submarine, some alien.
But even in a given spot, you can see from the way that
formations change as you go up and down across an exposure.
For example, there is a huge variation, what accounts for
that in a given place and how does that wind up affecting the
rocks and how they appear and how strong they are?
One of the big factors in the Colorado Plateau again, is the
ancestor Rockies. So prior to that time, period
things were relatively quiet and the plateau was fairly close to
sea level. So further west when you were
little bit deeper water and so you have things like the mauve
Limestone which is prominent Cliff former in the Grand Canyon
and you go a little further east and you find some fairly thin
Shoreline deposits and some Coastal deposits.
AS Global sea level changes, of course, you can get these little
variations but then you throw in something, like the ancestor
Rockies. And they start to erode that
material has to go somewhere. And one of the places we went,
was the Colorado Plateau. And so, the vast pile of red
rock that, you find in Monument Valley that you also find in the
Grand, Canyon, the soup. I group those sedimentary rocks.
Are basically because you now have this big source of sand and
gravel and mud. Mud that was flooding across the
landscape as those mountains finally.
Were worn down, roughly, 250, million years ago, then you
started to see The Return of the oceans coming back into parts of
the plateau. Similarly much later on the
modern Rocky. Mountains were created.
Starting roughly 75 million years ago, and as part of that,
the river systems were disrupted and we ended up with some very
large lakes. One of those large lakes is
actually the Words of the sedimentary rock that we have in
Bryce Canyon. So it's been a mix of
broad-scale global changes some local changes because of
tectonic activity. Okay.
So let's talk about the second phase then about what's happened
since these sediments were originally laid down in order to
get a rose in the very first thing you need is elevation.
If the rock is sitting down near or below sea level, not much is
going to happen. Once you've managed to graze The
Rock on up, then erosion is going to be able to act on it.
There's two different aspects of that the main one really for our
purposes is physical erosion. So it's basically the weathering
breaking down the Rock and then transporting it away as a Roshan
and different kinds of rock will behave differently.
So, the floovio sandstones and mudstones typically, they're
very thin bedded when you look at them at kind of will look
like grub Ali. Slopes Then these chance, he's
those sandstones tend to be quite massive.
You see what's called cross-bedding in it, which comes
from actually Frozen sand dunes. Basically that have been
preserved, and that material tends to form large Cliffs, the
limestone's, and some other things like conglomerates, which
are much coarser than the sand Stones.
Those tend to be far more resistant, they'll be ledge
Farmers, but they're typically not very thick.
So, irosian the physical erosion of this material results in
different looking things. The other thing that's
important, I think for a lot of people is really the diversity
of colors. So for instance, we have what's
called, The Painted Desert, which is just to the east of the
Grand Canyon, this is actually the Chinle formation and it's
largely. So colorful, in the case of the
Chin Li is because of volcanic ash deposits, which have lent
colors from, not only from, I Iron which is the most common
Rock coloring agent about from manganese and copper and
occasionally some other metals which will give you the pinks
and Maroons and some greens and even some bluish looking Rock,
most of the Red Rock though that you see it's iron and that iron
has been oxidized. It's been rusted, the iron might
have originally been in the rock as little grains of magnetite.
It could have been deposited as hematite.
There are some other mineral grains that are iron rich The
key thing though is that you need these deposits to have been
made in an environment where you have oxidation, which is
typically going to be at or above sea level.
So, in particular, the really Red Rocks, say at the base of
the Pinnacles in Monument Valley.
Those tend to be fluvial sediments, they were deposited
by Rivers. So The Rock was basically being
exposed the muds before it became Rock, was being exposed
to the atmosphere. These things.
Weathered into these very very red colors which are now
exposed. And so most of the red rock that
we have in the Colorado Plateau has been produced in that
manner. But there are places where the
rock is kind of whitish. Is that a different environment?
Yeah, in particular, the case of the Navajo is kind of
interesting. So again, the Navajo is what
forms the tremendous cliffs in Zion National Park and you'll
see both red and white colors in the Navajo, pretty much.
With the white above the red and for a long time geologists
argued about just exactly whether the Navajo started white
and was stained red. Whether it started red and was
bleached white. I think starting red and
bleached white has got the best support.
And the interesting thing is that what would do this is if
you had a reducing environment one which is the opposite of
oxidizing, and it turns out that if you have Petro chemicals
petroleum and gas and other sort of organic, And that move up in
the Rock, the Navajo Sandstone is actually a very porous
Sandstone. It's what we would consider an
aquifer. So, as petroleum is released
from some underlying say, limestone's it rises up and it
maybe gets trapped in the Navajo Sandstone above.
It is something called the temple cap Limestone which then
prevents any further upward motion of these fluids, the
fluids being reducing change the color of the Rock from red to
White. So it's been Suggested, I think
with good evidence that a lot of the white Navajo Sandstone that
we find in the southwestern, us used to be a big oil Reserve.
That subsequently was breached by erosion, all their oil and
gas went to the atmosphere, went into the surface waters and
we've, now been left with these different colors.
Was there any particular Confluence of circumstances that
led to the formation of the incredibly dramatic rock, towers
in Monument Valley The big thing that is true in Monument Valley
is first, you have at the bottom, the very bottom you have
a fairly resistant Rock unit that provides a base and sitting
on top of that are some fluvial deposits which is basically the
organ rock formation and then you have this and see the desha
sandstone and the trick of course, with this sort of Cliff
former, is that the way? I sometimes?
Think about it. If you went to the beach and you
had sand and you had for some reason, a pile Dominoes and you
set them up on end, kind of like, if you're trying to knock
over a whole series of dominoes, but you actually bring them
close together. So that they're actually right
up against one another, they'll sit there just fine.
So long as the sand is sitting underneath it, but if you start
digging away at the sand at the edges of Domino's, basically
start to fall in as the base of they sit on basically starts to
become unstable and that's kind of what happens with these big
Cliff warmers is that as long as you have something firm
underneath Neith, they'll support these tremendous Cliffs,
but the moment you start to eat away at that material
underneath, then they fail sometimes quite dramatically and
still preserve a cliff. So, as the cliff Retreats it
stays this big vertical, cliff and that variation in the style
of the rock. That was deposited going from
the much more muddy fluvial. Rocks of the Oregon rock that
sits below the deshays and stone transitioning to the Big thick,
just pure sand aeolian, sand, stones of the desha gives you.
That wonderful contrast that gives you this.
Incredibly dramatic and iconic typography.
I'm about six out because all around it.
The Sandy based became unstable on the Rocks.
Just fell away and have been washed away by Rivers.
Is that right? Yes, that would be accurate.
And what about the massive cliffs in Zion, or the Pinnacles
and Bryce. So the Zions very much, the same
as Monument Valley that's younger again in terms of the
Navajo Sandstone is younger than the stuff in Monument Valley.
And in fact it was probably one of the largest sand Seas on
Earth. Zion is about the thickest of
the Navajo. Sandstone, the case there is
that you have the K into formation underneath which has
almost exactly like the organ Rock in terms of it being a
fluvial deposit that can be eroded away.
The neat thing about Zion is that as you walk Upstream, if
you go Upstream in the main Canyon eventually, the walls
come together and you can walk up the Narrows of the Virgin
River. The Virgin River is the river
draining Zion and you can reach places where you can reach
across and you could touch both sides of the Canyon from one
spot. And when you're doing that
you're now standing on the Navajo Sandstone you're no
longer standing on any of the underlying sedimentary rocks.
And so that's a place where the Strength of these sandstones to
resistance. Basically, to collapsing really
stands out, you know, there are places in the Narrows, you look
up and you cannot see the sky because it's basically this slot
and these kind of slot, canyons are relatively common.
In the Colorado, Plateau Bryce is a much younger story and it's
different because in Bryce you have what are called hoodoos.
So, the thing that stands out about Bryce aside from the
colors, which are these bright oranges, Are these Pinnacles.
And in this case, you're dealing with a differential resistance
to weathering, that's present in some of the layers.
So some of the layers are Lake deposits there really to a
geologist or sort of ugly, they're actually kind of hard to
interpret because they were altered a fair bit after they
were deposited, but part of that was that some areas are cemented
in some areas aren't and there's a bunch of cracks.
We call them joint to indicate, there's no real motion across
Cross them, and these cracks act as places where weathering
proceeds very rapidly. And then in between the cracks,
weathering is much slower. And as a result, if you have
cross-cutting sets of these joints, you end up then with
isolated Pinnacles and depending on how efficacious the erosion
is. And the case for Bryce, it's
basically a steep-sided Amphitheater, where erosion
works very, very well. You flush away all the material
that's between these Pinnacles in your Then with these dramatic
Hooters. Okay, so turning now to the
third and final phase that you mentioned, the reason the rocks
are in plain sight from Horizon to Horizon is because this area
is, so extremely arid and nothing can grow, why is it so
dry? There's two pieces to that one,
is that we're kind of on the edge of the global desert built
that you find near the Tropic of Cancer.
So you're not quite up into the big wet part of the higher
latitudes, but a huge part of it is that the Colorado Plateau is
surrounded by mountains that are significantly higher than it.
So, storms at this latitude tend to come from west to east
through the winter and what those storms encounter to the
West is the Sierra Nevada. And this year, Nevada does a
perfectly fine job of earning its name by scraping off a lot
of the moisture. So very little is actually left
and even what little is left then encounters what are called
the high plateaus at the very west side of the Colorado
Plateau and the high plateaus scrape off a little bit more.
So when you get in the interior of the plateau, there's very
little moisture making its way there.
Now, there are times of the year where you do get storms, moving
from east to west. Those of us who live here on the
east side of the Rockies actually.
See this typically in early spring where moisture coming,
maybe from the Gulf of Mexico. Chicago's trying to work its way
west. And again, in encounters
mountains, it encounters the Rocky.
Mountains, Rocky Mountains, again, scrape off all the
moisture as they are good falls down the other side, it dries
out and again the Colorado Plateau kind of gets conked out
of any significant moisture. The last Direction where you
might get moisture is from the South during the Summer monsoon
season. There, you run into What's
called the Mogollon Rim, which is not as high as this year in
Nevada, or the Rocky Mountains, but it's still higher than the
bulk. Of the Colorado Plateau.
And so, once again, you tend to scrape off the moisture that
might be coming in from the Summer monsoon.
So a little bit, is the global environment that the Colorado
Plateau finds itself in. But an awful lot of it is that
despite the fact that it's well over a mile and elevation in
large parts of the plateau, it's surrounded by higher Rock,
higher mountains that basically prevent any of that moisture
from sneaking in. Okay, let's turn to our second
area of moviemaking Fame. The misleadingly named Alabama,
Hills in the Southern California Sierra, Nevada mountains, its
proximity to Hollywood made it extremely popular with film
directors and over 300 films were shot there.
Such as High Sierra, with Humphrey, Bogart, Django,
Unchained, and many episodes of The Lone Ranger series, not to
mention tongue. Of truck and suv ads that were
shown on us television. This must be a completely
different geological story. Yeah and indeed it is almost all
the rocks that you find in the Alabama Hills and this year
Nevada that sits behind it are granite's or Granite towards
where do these granite's come from typically.
What you're looking at is subduction of an oceanic plate
underneath the edge of the continent, as that water
saturated oceanic plate. The water is bound in minerals,
they become Unbound as you get to certain pressures and
temperatures. Water that then Rises off the
subducting slab. Interacts with the overriding
mantle melts, the mantle much as throwing salt onto ice will
cause the ice to melt throwing water into the mantle causes the
mantle to melt yielding Magnus that rise up into the crust.
And you end up creating volcanoes such as Mount Saint
Helens, Mount Rainier in the Pacific Northwest today and
underneath them. You produce these granite's.
So we're basically looking Being at one of the longest-lived
volcanic arcs in the world at least over the past 500 million
years is the volcanic Arc that's existed in this year.
In Nevada, from something like 320 million years ago to about
80 million years ago. Okay?
So what's happened to this Granite since it was in placed,
so there's grants crystallize a depth.
The way that you get the nice big crystals, that you can see
in a granite, is by having a lot of Time for the minerals to get
organized. And so you need to be at some
significant depth, some of the shallowest of the granite's may
have been at just five kilometers below.
The surface somewhere is deep is almost 30 kilometers below the
surface. Well they're not at Great depth
anymore so you had to actually remove a lot of the material on
top for the most part that was done by erosion.
Well rose on top, were the volcanoes.
So the lavas and tephra is, and other volcanic materials.
Those were far More easily eroded.
And most of that material was removed by about 60 65 million
years ago. Subsequent to that you start
seeing in the sedimentary. Rocks the transition from the
volcanic materials being eroded to the granite's, being eroded
off. Again, in order to have erosion,
you have to have elevation certainly in the late.
Cretaceous say 70 to 75 million years ago, the Sierra Nevada had
to be high the big questions been since then exactly what's
happened. This actually leads us into a
little bit of controversy, there's two camps, basically one
that thinks the Sierra, Nevada has stayed High much like it is
today pretty much since 70 million years ago.
And the other Camp feels that the range was lower.
It eroded down and eroded down and ended up to be significantly
lower than it is today. And is subsequently risen up in
about the last 10 million years. If the evidence can be
interpreted to mean It was a fairly sudden uplift over a
certain period of time. This reminds me a little bit of
what Peter Molnar was talking about in his podcast to explain
the rapid uplift of Tibet. And I'm wondering if the seismic
imaging under the Sierras is good enough to see if there's a
piece of mantle that might have dropped off, that could be
implicated here. Yeah.
So, I mean those of us who are inclined to think that the range
is Young point to an anomaly, that long ago, I called it the
Isabella anomaly, and that name is stuck.
So this is a high-velocity I've lost in the sense of the speed
of seismic waves through the material body that sits in the
upper mantle going down to depths of around 300 kilometers,
underneath the South Eastern, Great Valley, the South Western
Sierra Nevada, and it turns out volumetrically that this Very
much like the material that would have sat underneath the
high part of the Sierra Nevada, 10 million years ago.
And unlike the situation in Tibet, our ability to image,
this is much better in the case of California in part, because
it's a smaller area. Logistically, it's much easier
to access. And, actually, the geometry of
earthquake sources for being able to do, tomography is very
good in California. So we have this, really
excellent image of this body. D, we also have evidence from
volcanic pipes that came up between 8 and 12 million years
ago, in this year in Nevada, that actually brought up pieces
of the uppermost. Mantle, in the lowest crust that
used to be present in this year in Nevada and that material.
Some of it is basically just garnet and pyrrhic scene.
So it's a garnet peroxy night. This material is very, very
dense. It's denser than the mantle
underneath it it's gone today when we do it.
Jing under the high part of the range.
There is none of this material present under the range today,
but the material in the Isabella anomaly.
The characteristics of it are perfectly compatible with that
Isabel anomaly containing a lot of this Garnet proximate.
So, it does seem like a weight in order to get the mountain
range to rise up as that you have removed.
This very dense material that sat at the bottom of the crust
and now you've just kind of poured it down this hole.
So it's on its way down into the mantle.
Let's talk a bit about the shapes of the landscape in
contrast to Monument Valley in the Colorado Plateau, we don't
see tabletop mountains, stepped Cliffs and the towers that we
see there. It looks really different.
The first thing is, of course, the granite is far more uniform
in its Behavior. You're not going to have, but
rubble, a slope, and then a big cliff and some capping thing
that is more resistant, it's all Granite.
But what really affects the way, the granite Rhodes has a lot to
do with the climate. So, if we go back to the Alabama
Hills, when you look at the Alabama Hills, it's these
rounded, knobs Chamber of Commerce, and Lone Pine likes to
tell them is the oldest Hills in the world, which is, This
they're not particularly old but they give you that kind of sense
that they've been there forever and they've been sort of rounded
and ground down whereas the exact same rock that sits up on
the crest of the Sierra Nevada. That's in the background of
those movies. It's forming, these tremendous
spires and a rat's, horns, all kinds of wonderful.
Very sharp Alpine kind of geometry that still the granite
but there is being affected by Ice rything A sure plucking
glacial erosion glacial polishing.
So the glacial aspects acting on the granite, give you these very
different shapes than what you're going to see down low in
sort of the desert where the Alabama Hills are by and large
that uniformity of the rocket tends to give you these nice,
beautiful u-shaped valleys which are classic shape that you'll
see in the Alps. You see them in much of this
year in Nevada, but the funny part about Here in Nevada.
Some places the granite is a little bit different so in the
Tuolumne drainage which is just North of Yosemite Valley, The
Rock, it's extraordinarily uniform.
And it has very, very few joints.
It has very few of these little cracks and so the glaciers were
not able to pluck any of the rocks out.
So when you look at the, What's called the Grand Canyon of the
to Olney, it's v-shaped, even though it had the thickest
Glacier in this year in Nevada, there was nothing for the The
glacier to do, but just polish it in contrast Yosemite Valley.
It has this amazing diversity of, lots of different kinds of
granite. And as a result, it has lots and
lots of different fractures and things in different places.
So that parts of it are extremely fractured parts of it
are not like El Capitan and that combination has allowed glaciers
to excavate to an extreme degree so much so that there are 2,000
feet of sediment that actually sits in the bottom of Yosemite
Valley. So the original Are you shaped
Valley has been filled in with sediment and so you have these
nice flat Meadows practically going up to the base of these
tremendous Cliffs and what about the Final Phase?
That present-day climate all the Rocks there in the Alabama Hills
exposed as in the Colorado Plateau, because it's a desert
where nothing can grown cover them up.
Yeah, certainly and the Alabama Hills, you are in one of the
biggest rain Shadows on Earth. The high peaks of the Sierra,
Nevada to the west or for over 4000 meters, the passes are
nearly 4,000 meters. So all that precipitation that
would be coming from the West get scraped off.
To the Alabama, Hills are very much desert.
It's extremely dry. Is it Mary Austin's book, land
of little rain was about Owens Valley and just the fact that
she chose to title the book that tells you just how that
situation is. In contrast the Closure in the
high part of the range is because of actually having all
of that moisture and having been in an ice age, a lot of soil got
scraped off. And you just have lots and lots
of bare rock, and there's only so much vegetation that can claw
its way into these bear. Granite Cliffs, what do you
consider to be some of the most important jalaja call problems
that have yet to be solved in the American West?
You know, I think it comes down to paleo elevation for
geophysicists elevation is what would call the zeroth order.
Observable. It is the most important basic
piece of information. And we kind of take it for
granted today, that you look around and you say, well, it's
yes, we can measure it, we can measure lots and lots of
different ways, but as soon as you get into the geologic past,
if you're much above sea level, it's really Hard to know how
high. So for instance, the argument
about the Sierra Nevada, if the Sierra Nevada is Young, and
we've created a young mountain range by removing dense material
at the base of the crust. That's important to know because
it's telling us about a process that we only see hints of in
other places, that could be very important in contrast, if the
range is really old, if it's been high, say 40 million years
ago, it was really high, then we have a problem that we need to
To understand how the range could stay that high.
Well things were changing so dramatically in the upper mantle
and lower crust underneath. So we look further afield,
there's arguments about the Colorado Plateau.
There's arguments about the Rocky Mountains and amazingly.
There is an argument about the high plains, which are here,
east of where I'm sitting in Boulder Colorado, you do are the
High Plains High where they high 60 million years ago or have
they just gone to their And elevation making Denver the mile
high city 5 million years ago and again knowing which of those
is really the case or something in between is telling us about
very large-scale Earth processes that they're not contradicting
plate tectonics but they're expanding upon it.
We're learning about processes that we don't really have a grip
on it present. It's really intriguing because
when you think of large flat areas, At least naively.
I would think of a flood plain, which would be very low because
it's got water flooding into it. And depositing, it or perhaps
something like Tibet Plateau, which is very high because if
you have something like some of the processes you are just
talking about. Making that Region anomalously
High although perhaps not on the same scale as the high plains so
are you thinking that there might be yet some completely new
process at work here? It certainly looks like there's
got to be something very unusual, the kind of processes
feel. For instance, dripping off the
lower crust and upper mantle like we see under this year in
Nevada, the scales of the high plains are too large, that's not
a process. That works at the scales.
We see of the high plains, we have hundreds of kilometers of
gentle gradient. Going down from the Rocky
Mountains down towards the Mississippi River.
So it's requiring something novel and ideas range from large
scale flow in the mantle having either pulled everything down
and piled up sediment and then pushed it back up to ideas about
changing the character of the mantle over very long
wavelengths by adding some water and creating less dense minerals
in the mantle to a kind of nutty idea that we've put forward a
few years ago where the water coming off of the old laramide.
Slab came up actually through the metal and made it into the
lower crust. Where the lower crust previously
had been rich in Garnet that. Garnet, would retrograde under
those conditions into less dense minerals and produce a very
broad uplift. So you know, these are the hooks
that I think those of us in doing research really look
forward trying to look for the things that you can't really
explain easily with the current Paradigm.
And I think the high plains These are really stupendously,
dramatic, example of that. Because a big difference with
say, the Tibetan Plateau is the Tibetan Plateau.
There's a tremendous amount of deformation and crustal
thickening. There are thrust faults all the
way across the Tibetan Plateau, the high plains are under
formed. There's no crustal, shortening
by thrust. Faulting, there's been no
physical deformation of it, the oil geologist who work across,
it is practically a layer cake of sediments that have
accumulated over the past. 400 500 million years.
So it's the kind of place where we learn new things about how a
planet can actually operate Craig Jones.
Thank you very much again. Thank you very much for having
me for more about geology, b, as well as pictures and
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