Hello, from what I think is one of the most dramatic and colorful landscapes on the entire planet.

♪ This is known as Red Rock country of the southwestern United States, and when you're here, you can't help but think like a geologist as you explore the region.

The geologic story at first seems incredibly complicated, but actually, it's a piece of cake.

♪ Everywhere you go, you see colorful, horizontal rock layers, exposed by rivers and streams cutting down through them, like a knife carving out a nice piece of layer cake.

There are few, if any, earthly landscapes like Red Rock country, with its beautifully sculpted rock formations, many sheltering ancient, indigenous rock art and dwellings.

I'm Doug Prose.

It'll be a blast going out and making sense of this incredible place.

Let's go explore.

[Theme music playing] ♪ ♪ Announcer: Funding for this program was provided by the National Science Foundation.

♪ Prose: Red Rock country is in the heart of the geologic province called the Colorado Plateau.

This province is quite large.

It's the size of the country of Germany, and it's so beautiful that it's home to 26 national parks and monuments, mostly preserving stunning geologic landscapes.

Each place tells a unique geologic story, but each is a slice of the larger geologic layer cake.

I love the layer-cake analogy for this region because, well, personally, I like eating cake.

♪ Prose: So let's start exploring Red Rock country in the incomparable Arches National Park, where seeing one arch makes you hungry to see more of the park's otherworldly shapes.

So we're going up.

♪ Climbing around on these rocks can be amazing, if not downright harrowing.

The rocks were created by the ravenous forces of erosion and a hidden ingredient that is also used to enhance the flavor of food.

To form all the arches here, the landscape had to be cracked apart into a lot of joints and fractures first, so, for that to happen, the process involved this.

[Maracas rattle] Far below the sandstone rock layer that features the stunning arches and tall shapes called thins, a different rock layer is permeated with salt, evaporated from seawater when this region was inundated by an ancient ocean some 300 million years ago.

That salt layer has made the surface a tasty feast for our eyes today.

The salt layer, when it got pressurized by the rock layers on top, it kind of turns to plastic, it actually starts to liquify a little bit, and that lets the rock layers on top actually start to crack apart and move a little bit.

As the sandstone above the salt layer split apart into long blocks, erosion by ice and water wedged into the cracks and patiently began sculpting wondrous shapes.

Happily, this intensely dissected terrain does not end at the boundary of Arches National Park.

It keeps going onto public lands, where anyone is free to visit them.

This is a place called "Behind the Rocks."

It's near Arches National Park, and not sure why they call it "Behind the Rocks."

It's a--it is the rocks, but anyway, it's sort of like Arches National Park in that the salt layer below the sandstone had a hand in forming the landscape and the beautiful jumble of cracked and fractured sandstone.

But for all the influence of erosion and subterranean salt, there is yet another, much larger geologic force that is behind the creation of Arches Park and all of Red Rock country, without which there would be none of this rocky splendor.

The big-picture geologic process that is operating under the Colorado Plateau here is the process of subduction, so I really need to draw you a graphic to show you how the subduction process works.

Oh, here's some paper.

Amazing.

OK, it's like this.

The subduction process under Red Rock country is unusual.

It involves the Pacific Plate, which carries the Pacific Ocean, colliding with the North American continental plate, 70 to 80 million years ago, then diving, or subducting, below it.

But instead of curving steeply into the earth's mantle, as is typical, the Pacific Plate slipped under the continental plate at a very shallow angle and put enormous upward pressure on the top plate as it wedged its way under it.

And that enabled the top plate-- the continental plate-- to move up, up, up, up, and get higher and higher and stay together as one crustal block and not break apart.

As the plateau rose, the Pacific Plate below actually broke off and sank deeply into the earth's mantle, clearing the way for very hot mantle rocks to push up the plateau even higher.

The latest phase of uplift began 10 million years ago and continues today, raising the plateau to an average height of over 6,000 feet, or 1,800 meters.

This is when the plateau's rivers truly sculpted the terrain as we know it today.

So the crust was able to stay together as one piece and let the rivers start cutting down very quickly and create these unbelievable canyons and arches and other shapes that you see here.

♪ It's the rocks and sediments exposed by the rivers and other forces of erosion that lends so much color to Red Rock country.

But how did the rocks form originally?

That's a geologic story that is somewhat less dramatic than subduction, and the best place to see that story is, ironically, in one of the most dramatic, gorgeous geologic wonders on Earth-- the Grand Canyon.

All right.

Prose: Wow.

All right.

You going to the bottom?

Yes.

I was gonna go all the way down to the bottom of the Canyon today, but this trail is just covered with ice and snow because it snowed like crazy last night, so it's just not gonna happen.

The Grand Canyon is quite unique in one aspect that I find kind of ironic, and that is, when you look out at the canyon walls, you're looking out at horizontal rock layers that were created in a very undramatic fashion.

Some of those layers are limestone, rocks that were originally soft sediments.

It was at the bottom of an ancient ocean that all these sediments were just really slowly building up over millions of years that eventually became those rock layers that we're looking at now.

Some of the layers are sandstone, like at Arches National Park, and those accumulated at or just above sea level.

Sandstone and limestone can look very similar.

Usually, only a geologist can tell them apart, but both accumulated and hardened extremely slowly, undramatically.

But then, geologically, a lot of dramatic things happen to lift those rock layers up and allow the Colorado River to slice down through them and expose them so we can see this.

The mighty Colorado River, which starts in the Rocky Mountains of Colorado, plays the key role in sculpting the Grand Canyon and, in fact, the entire Colorado Plateau.

I'm in your way?

Here, I'll move.

I have some friends down here.

[Chuckles] You want to hear a story about some geology?

Here, I'll tell you.

So, the sculptor of the Grand Canyon is the Colorado River.

Well, the Colorado River-- if it wasn't for the Colorado River, there would be no Grand Canyon, there'd be no Red Rock country, there'd be no beautiful red and white and pink and orange cliffs for all of us around the whole world to come and marvel at.

What do you think of that?

Heh!

Over 90% of other rivers and streams on the Colorado Plateau drain into the Colorado River, and each is cutting its own way into rocks, carrying the eroded sediments downstream.

And they're doing that with the help of gravity, rain, snow, and ice, which are working to push and pull them down, down, down, down, and ultimately, they will end up in the Colorado River.

But for now, there is still plenty of rock left in Red Rock country, so let's climb to the highest rock layer on the Colorado Plateau-- the Book Cliffs.

There's a beautiful stack of books behind me made out of rock, and those are the Book Cliffs.

This sandstone cliff runs for more than 200 miles, or 320 kilometers, making it one of the longest cliff faces in the world.

So, if you picture the Colorado Plateau as a layer cake of rocks, the Book Cliffs are kind of like the writing on top of the icing.

♪ And now, for the icing itself, which is actually the topmost layer in a special geologic area called the Grand Staircase.

You can treat yourself to this famous layer in Bryce Canyon National Park.

This is Bryce Canyon.

It's such a lovely National Park.

It's at a high elevation, about 8,000 feet at the rim, and so that puts it at the top of the Grand Staircase, or the layer cake, so it's the frosting layer here.

From Bryce's lofty rim, the rock layers step down in dramatic fashion to the east, revealing why this area was named the Grand Staircase.

But where is the canyon named Bryce?

It's not really a canyon; it's actually the side of a high plateau, and then the eroding forces of ice, wind, and water began working on the exposed rocks on the side of the plateau.

Bryce's highest rock layer, at its rim, is one of the most stunning sights on the planet.

This is the topmost rock layer of Bryce.

Beautiful layer.

It's got the hoodoos, the fins, the queens, the humans, the alligators.

That's because it's a very soft rock layer, and it's soft because, first of all, it was laid down in a lake environment, so it's very muddy, soft sediments to begin with.

[Bird cawing] Also, we're at one of the topmost layers in the Grand Staircase, so it's one of the youngest layers.

And being so soft, the layer has been relatively easy to sculpt by the talented artist of erosion.

Little creeks, like this one at Bryce's lowest and oldest layer, carry off the eroded sediments in their sparkling waters.

♪ [Grunts] I'm at the bottom of Bryce Canyon National Park right here, and this is one of the creeks that drains out of the park, and it's a pretty small creek.

It's only maybe 8 inches deep, but these little creeks are responsible for carving that dramatic scenery that you see back up in the park.

It's amazing because you can just imagine how much time it took to do that.

Bryce's oldest rocks, which are sandstones, are shared with another incredible National Park in a peculiar way.

So the oldest and lowest rock layers in Bryce Canyon here are the highest layers in Zion Park, which is not too far that way.

♪ Only 80 miles, or 130 kilometers' drive from Bryce, Zion National Park is at a lower elevation, about halfway down the Grand Staircase.

If you picture the Grand Staircase as the big layer cake, we're in about the middle of the layer cake here in Zion.

It's the middle icing layer, which is the sweetest part of the cake, and when you have a place like this, it's one of the sweetest places on the entire earth, if you ask me.

The best way to experience the geology here is to climb on it.

Scaling Zion's sandstones, it's neat to picture dinosaurs padding across these same surfaces, except they were traversing soft sand dunes 200 million years ago, before the dunes hardened into sandstone.

[Wind blowing] What's interesting to me is I'm standing here, and sand particles are actually blowing off of this sandstone and, like, hitting my skin.

It kind of stings a little bit.

So that means that the sandstone is eroding, and eventually, it's gonna all erode down and turn into soft sand dunes again, all over again, so it's sort of like geology is repeating itself here.

Besides wind, you can also get in direct contact with the other, more significant force that is sculpting Zion's rocks-- water.

So I'm standing in the Virgin River.

It's very cold-- it's about 65 degrees, so my feet are numb-- but this is a classic example of downcutting by a major river into the Colorado Plateau.

And the eroded materials will be carried down the Virgin River and eventually will make their way into the-- you guessed it-- Colorado River.

So a fun way to picture the layered geology of the Grand Staircase is to become a giant.

If I were a giant and I wanted to descend the Staircase, I'd go over to Bryce Canyon National Park, and I'd start from the top there, which is the top of the Staircase, and I'd take a few steps down the rock layers, down to the bottom of Bryce Canyon, and then I'd move over a little bit and be at the top of Zion National Park.

Then I'd take a few steps from the top of Zion Park to the bottom and then move over a little bit, and I'd be here, at the top of the Grand Canyon, the same rock layer.

But we're not giants, and that's a good thing, because there is so much for us regular-size humans to experience in Red Rock country between the top and bottom steps of the Grand Staircase, like threading your way through a slot canyon.

I'm standing at the beginning of an amazing slot canyon called Spooky Gulch, and it's said that the name came from a school group who hiked through here many, many years ago on Halloween.

[Indistinct chatter] And that's really neat because this is the week of Halloween right now, so that's when I'm gonna go up the canyon, too.

The many slot canyons in Red Rock country are like miniature versions of the bigger canyons, formed by the same downcutting power of running water.

Luckily, I'm pretty slim because some of these are really narrow.

Gosh!

[Grunting] Whoa.

They're definitely narrow.

Fabulous slot canyons are carved into a peculiar geologic feature called the San Rafael Swell in central Utah.

So this canyon, about 500 feet deep.

This is a really long one here, so I'm gonna go back in there and see how far I can get.

It's really narrow.

The slots are downcut so deeply partly because the San Rafael Swell's rock layers rose up differently here than they did elsewhere on the Plateau, as subduction lifted the earth's crust from below.

When the earth's crust was pushed up by subduction, this part of the crust warped up a little bit and made kind of a--a bump, and it's not really a swell because a "swell" implies that it grew outward as it grew upward, but it didn't; it was actually compressed and pushed upward from both sides.

The Swell's slot canyons came in handy for an infamous historic figure who lived here in Utah.

I can't really talk about the San Rafael Swell without talking about Butch Cassidy.

Butch Cassidy and his outlaw gang would rob banks to the west of the San Rafael Swell, then he would escape on horseback through the San Rafael Swell.

[Imitating hooves clopping] [Grunts] Come on, you guys.

Hurry up.

Ha ha ha!

There's another up-warped piece of the earth's crust in Red Rock country, this one with a gorgeous, serrated cliff called Comb Ridge.

This is Comb Ridge, and it's really an interesting geologic feature.

The earth's crust kind of up-warped here a little bit, and a little creek that runs on the west side of the ridge just kept running and running along this little up-warped part of the crust until it eroded a big cliff.

Comb Ridge is part of Bears Ears National Monument.

Besides being geologically special, it is very important culturally to the indigenous people who have been living in this region for thousands of years.

The neat thing about the ridge is that there were a lot of people living around here, and the ridge made for a beautiful place for constructing cliff dwellings.

So this is the trail to one of the really cool ancestral Puebloan sites on Comb Ridge.

Here we go.

Many of the ancient sites are tucked into narrow canyons on unmarked trails.

Some of them are more than a thousand years old and must be visited with extreme care.

The rocks of Comb Ridge were used by the ancestral Pueblo people for building and shielding dwellings, but the rocks provided more than shelter.

So these petroglyphs are carved into the surface, called desert varnish, and what desert varnish actually is is a living crust of lichen, and so, when water runs down here, it actually provides enough water for little, teeny lichens to grow on the entire surface and turn it dark brown.

Tiny particles of clay that includes minerals like manganese and iron are mixed with the lichen to form the dark, rocky canvas for the petroglyph-makers.

The way they know that these things are old is that there's varnish developing inside the petroglyph, and it's quite developed, so it takes hundreds and hundreds of years for that to happen.

Comb Ridge is near Bluff, Utah-- one of the oldest villages in North America-- and just down the road are places where erosion has sculpted especially dramatic landforms out of the layer cake of rock.

One place, also part of Bears Ears National Monument, is called the Valley of the Gods.

Here in the Valley of the Gods, we've got all these rock shapes sticking up, kind of isolated, and they were all once one big rock formation that has been eroded slowly but surely by streams and ice and wind and rivers, and now you've just got these amazing shapes.

Speaking of rivers, a rather extreme example of downcutting river erosion suddenly appears just south of the Valley of the Gods.

The San Juan River is down there, cutting this unbelievable canyon, which is called the Goosenecks.

The reason it's so windy right here is because initially, before there was tectonic uplift, the river was windy already, and the uplift was so fast that it retained its windiness.

There are countless, stunning rock formations and canyons to explore in Red Rock country, like this one, resembling a sombrero.

Well, I'm getting tired of wearing this hat, so I'm just gonna put that one on behind me here.

[Grunts] How's that?

Besides rock layers, there is another geologic feature that is common in Red Rock country-- volcanoes.

The latest eruption occurred here near Flagstaff, Arizona about 900 years ago, and it caused the indigenous Sinagua people to move their cornfields around after the eruption stopped.

These volcanoes are in the San Francisco volcanic field.

So geologists think that in the future, they'll be the next ones to erupt, and that could happen at any time.

[Hissing] It was the study of ancient volcanic features that led to the discovery of a very peculiar geologic event that occurred long ago on the Colorado Plateau.

Wow!

That's really hot.

That's probably 110, 115 degrees.

This is the Hot Springs near Monroe, Utah, and it's right in the middle of the Marysvale Volcanic Field, which is one of the biggest volcanic areas in the southwest United States.

♪ Here.

[Grunts] Oh, there's a hot pool down there.

Can't pass this up.

Millions of years ago, there was a gigantic volcano right over there that was as big as, like, Mount Fuji in Japan or maybe Mount Shasta in California.

And it spewed lava and ash many dozens of times all through the eons, and you can still see the thick layers of lava and ash in the hillsides all around here.

And then, about 23 million years ago, an incredible thing happened here.

All the lava and ash that was sitting here in a big pile suddenly collapsed and just took off that way in a gigantic landslide.

Now, this landslide was huge.

The landslide was some 60 times the size of Manhattan.

It was a whopping 60 miles long, or about a hundred kilometers.

The landslide went 100, 200 miles an hour, and if we were sitting here and we took off on that landslide, that would have been one heck of a ride.

But not to worry.

The Colorado Plateau has settled into a mostly stable, rock-solid land in the many millions of years since that landslide.

So come on out to Red Rock country, and when you're here, you will find a geologist within you come alive as you take in this rocky Utopia.

♪ [Theme music playing] ♪ ♪ ♪