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>> Earth, a unique planet,

restless and dynamic.

Continents shift and clash,

volcanoes erupt,

glaciers grow and recede--

titanic forces that are

constantly at work,

leaving a trail

of geological mysteries behind.

And there is nowhere more

mysterious than Death Valley,

the hottest and driest desert

in the United States.

This is a place where even

700-pound rocks appear to move

by themselves.

It's the lowest point

in the U.S., and right here,

the earth's crust is thinner

than almost anywhere else

on the planet.

Death Valley is a dynamic

laboratory for investigators

who uniquely read rocks

like x-rays to reveal

the inner workings of the Earth

and its history...

adding to the continuing story

S02x09 Death Valley Original Air Date on January 26, 2010

-- Sync, corrected by elderman -- -- for MY-SUBS.com ---

Death Valley is the largest

National Park in the lower 48

states, more than 3 times

the size of Rhode Island,

straddling the border

of California and Nevada

and surrounded by towering

mountain peaks.

140 miles long

and up to 15 miles wide,

with temperatures reaching

a scorching 134 degrees

fahrenheit, this is one

of the most inhospitable places

on Earth.

[rattlesnake hissing]

But for geologists, Death Valley

has a unique attraction.

Here they can witness

the interplay of the Earth's

most titanic geological forces.

>> When you look at Death

Valley, really you're looking

at a battle, a battle between

processes that are occurring

on the earth's surface,

and we can see the record

of those forces of nature

locked into the rocks.

Death Valley has an archive

that is almost unrivaled

worldwide.

>> To uncover Death Valley's

earliest history, Prave is

hunting for its oldest rocks.

He is searching in one

of its most remote spots,

in the extreme south

of the valley in the isolated

Alexander hills.

>> This is one of the oldest

rocks in Death Valley.

It's 1.2 billion years old.

And given the color of this rock

and the fact that it's

quite soft--it can powder

when I scratch it--

These are all clues that tell me

that this is a limestone.

>> The limestone is a major clue

to revealing the way

this arid desert used to look.

>> If we think about the type

of environments that limestones

can be deposited in,

the first that comes to mind

is an underwater

and a marine setting.

>> There is only one way

to form limestone.

It is made from the tiny bones

and shells of sea creatures.

They die and sink to the sea

floor, where the weight

of further layers on top of them

crushes them slowly

into solid rock.

And Prave has discovered

other startling evidence

that Death Valley had

a watery past.

>> Fossils are a major clue.

They are vital in the type

of evidence that a geologist

will use. And these are

some very nice examples

of the type of fossils

that you can find

in these ancient rocks.

And you can see here

these curving surfaces

outlining what look to be

large cabbages that are

sliced in half.

These were algae

known as a stromatolite.

>> Ironically, these marine

fossils have survived

in the Death Valley desert

only because there is

so little water that might

otherwise have washed them away.

But they would have originally

looked like this

when they flourished

in the Death Valley waters

as the limestone formed

more than one billion years ago.

>> These tell us that

the environment when this rock

formed would have been

a shallow sea.

If I'd been here when these

rocks were first being formed,

I'd be sitting in my swimming

trunks about waist-deep

in water, very much

like the Bahamas today.

>> The stromatolites are

some of the earliest signs

of life on our planet.

To discover what happened

over the next one billion years,

Prave studies evidence

in the surrounding hills.

>> The different bands of colors

and the rock layers in the hills

represent ancient seas that

covered the Death Valley area.

The seas would deposit

a layer of limestone,

move back across the land.

Another layer of limestone

would be deposited.

And so we have a history

of the seas moving across

the Death Valley region from

the time of the stromatolites

to these rock layers now,

more than a billion years later.

>> Geologists wanted to

figure out what dramatic

geological upheaval could

have turned Death Valley

from a shallow sea to the

baking-hot desert of today.

And Prave has found clues

in a rock that is entirely

different from the marine

limestones he has studied

up until now.

>> This is a nice example

of a rock type called a granite.

And it forms those veins that

are in the hillside behind me.

You can think of these

like the fingers of my hand.

They're fed upward from

a much more larger, massive area

of granite sitting underneath.

>> The granite tells scientists

the reasons why Death Valley's

ancient seas vanished.

Today, it is solid rock.

But it was once hot molten magma

from deep underground.

Only one force of nature

has the awesome power

and 2,000-degree fahrenheit heat

to melt rock into magma

and fire it to the surface...

Volcanoes.

The seas here didn't

just drain away.

They were pushed back

by these mountains of fire.

It was only in the 1960s,

with the realization

that earth's continents

were drifting around the planet,

that scientists figured out

why the volcanoes erupted

under Death Valley.

The theory of plate tectonics

revealed that around

100 million years ago,

an ancient oceanic plate began

sinking under North America,

pushing up the land.

Heat from the collision powered

a coastal chain of volcanoes,

erupting on the land and finally

driving away the seas

submerging Death Valley.

>> This landscape would have

been very explosive, a hostile

type of setting.

And that then set the stage

for what was to become

Death Valley.

>> Still surviving in the valley

to this day is the ghost-town

evidence of another substance

far rarer than granite

that the volcanoes

grought to the surface...

gold.

Although gold occurs naturally

in more than 30 different

U.S. States, the gold

in Death Valley was concentrated

in veins in the rock, as magma

solidified near the surface.

It made it worth mining,

and millions of years

after its formation, it sparked

the Death Valley gold rush.

>> This is a wonderful example

of a gold mine shaft.

It's the Eureka mine, high up

in the Panamint Mountains,

associated with trying to find

gold in the granites that were

intruded into these rocks

100 to 200 million years ago.

The gold would have been

in veins, these fingers

that would have been injected

up into these rocks.

And the gold would have been

concentrated in these veins.

>> The gold rush here lasted

just a few years.

Miners often had to remove

a ton of rock to recover

only 1/10th of an ounce of gold,

enough to produce just a single

wedding ring.

Today, all that remains are

empty tunnels and ghost towns.

>> It's interesting to consider

that the frenzy of activity,

mining gold, was actually

a direct result of the kind

of volcanic activity

100 to 200 million years ago.

>> Geologists investigating

the battle that raged

in Death Valley between fiery

volcanoes and ancient seas

have found important evidence.

Stromatolite fossils are proof

that Death Valley was once

submerged by the waters

of a shallow sea.

Veins of granite could only

have formed in the fiery heat

of the volcanoes that burst

to the surface around

100 million years ago

and drove that sea away.

The volcanoes built up the land

that was to become Death Valley

into peaks as high

as the Cascades Mountain range.

But deep beneath the Earth's

surface, awesome geological

forces were about to destroy

those peaks, stretch the land

apart, and transform

the mountains of Death Valley

into the lowest point

in the U.S.

>> For a billion years,

Death Valley remained

a flat plain under the sea.

Around 100 million years ago,

erupting volcanoes formed

high mountain ranges.

But then the real geological

mystery began. The land here

must have undergone

an extraordinary transformation

because today in Death Valley,

those high mountain ranges

have vanished. Incredibly,

the one-time mountains

have sunk below sea level

to become the lowest point

in North America.

Yet all around the valley,

snow-capped peaks still soar

up to 11,000 feet into the air.

The investigation digs deep

under the landscape to discover

what vast geological forces

could have caused

that huge difference in height

between two places just

20 miles away from each other.

>> There are a lot of

mysterious aspects

about Death Valley.

It's a unique landscape,

because the valley floor itself

is very deep.

It's below sea level.

And the mountains rise up

very steeply on either side.

>> Clues to the power

of these underground forces

lie all over the valley...

If you know where to look.

many of the rock layers

were originally deposited

on the ancient flat sea bed.

they can still be seen

as horizontal layers.

But other nearby layers

aren't horizontal at all.

They tilt downwards

into the ground.

Miller finds a further clue

of earth's power in the unusual

shape of this cinder cone,

a mound of ash and debris

lying on Death Valley's floor.

>> It looks like it's

two cinder cones, but in fact

it's really just one

that's been pulled apart

along a big fault zone.

This has moved some 700 feet

in some 700,000 years.

So that's about a foot

per thousand years,

which sounds like it's

really, really slow, but if you

look at it over a great length

of geologic time, you get

quite a lot of slip.

And give it even longer time,

it will be offset even more.

>> Miller's next challenge

is explaining what is making

the fault line move.

For that, she studies

other ancient rock formations

whose jagged outline has given

them the name turtlebacks.

>> The turtlebacks are crucial

to understanding Death Valley's

early origins. They have so much

of the record here, if you're

willing to spend time

to try to unravel it.

>> The real clue lies in

the rocks' distinctive texture.

>> If you just take a look

at this rock closely,

you can see that it's

very kind of strung out,

very stringy. It tends to be

pretty fine grained.

>> This texture tells Miller

where these rocks came from.

>> We see evidence that these

rocks were deformed,

just like if you'd take

a piece of plastic

and were to heat it up,

you could bend it.

It's the same thing with rock.

And so these rocks formed at

high temperatures and pressures

within the earth's crust

at depths of about 10 miles

or so, and they have since been

brought to the earth's surface.

>> Miller concluded that some

overwhelming underground force

must have raised the turtleback

rocks to the surface

and stretched them out

like warm toffee

as Death Valley formed.

The final explanation

of what happened here

once again came back to the way

continents drift around

the globe.

As the collision of the plates

that had forced ancient

volcanoes to the surface

slowed down and ceased,

the high mountains that once

dominated the land were slowly

pulled apart and tilted

downwards.

Gradually, as the underlying

crust grew thinner and thinner,

a deep basin formed

between the mountain ranges.

Death Valley is the most extreme

example of what such stretching

forces can do.

By measuring seismic waves,

scientists discovered that here

the continental crust

is just 16 miles thick.

This might sound like a lot,

but it is far thinner

than almost anywhere else

on the planet.

Around the globe,

the earth's continental crust

averages 25 miles thick.

It's strongest beneath

the Himalayas.

At 43 miles, thick enough

to support the weight

of massive mountains

such as Everest.

The turtleback rocks

also offer Miller evidence

as to when Death Valley's

stretching started.

Dating these rocks reveals that

the deformation started here

around 13 million years ago,

although Death Valley did not

take on its final shape

immediately.

>> Death Valley's really young

when you look at the whole

geologic time scale.

Modern Death Valley is probably

3 or 4 million years old

at the most. The stretching

started before that.

But Death Valley itself

is a very recent feature.

>> Scientists know that the

process is far from finished.

They've found irrefutable

evidence in the alien

Death Valley landscape

known as Badwater Basin.

>> I'm standing here

at Badwater, which is

the lowest point

in the western hemisphere.

It's 282 feet below sea level.

We're actually standing

below sea level about the depth

of a football field.

This floor has been sinking.

It's about a tenth of an inch

per year, which is about

half of the speed at which

your fingernail grows.

>> Continual stretching

of the earth's crust

has turned Badwater

into one of the lowest spots

on any continent on the planet.

Yet its true depth

is even lower still.

>> The surface that we see here

is the present-day surface.

But what one has to realize

is that beneath our feet,

we can go down through sediment

that represents ancient periods

of time, when Death Valley

was a surface that goes down

3 miles.

>> You would need to drill down

through the sediment

to a depth equivalent

to 11 Empire State buildings

end to end before you hit

the crustal bedrock.

The total volume of material

in this basin would bury

New York to the depth

of nearly a mile.

The valley floor is constantly

being covered with sediment

cascading from the surrounding

mountains, but it can never

fill up completely.

>> The sediment is coming in

at a rate that is less than

the rate of sinking

of Death Valley itself.

So that we're always maintaining

a surface here on the valley

that is sitting below sea level

and is continuing to sink

through time.

>> This constant movement

shows Earth's geological forces

at their most dynamic

and makes Death Valley unique.

>> The allure is that nowhere

on earth do we see continental

crusts being pulled apart

at this rate or this magnitude.

>> The investigation into

Death Valley's creation

has established how it sank

to become the lowest point

in North America.

The turtleback rocks were

deformed by the powerful

tectonic forces pulling

the mountains apart

to form a wide valley floor.

The still-sinking landscape

of Badwater, currently 282 feet

below sea level, is proof

that the crust here

is still being stretched today.

But the sinking of Death Valley

is just one part of the story.

Geologists still need

to investigate how one

of the hottest places on earth

was shaped by the power

of moving ice.

>> 1.2 billion years ago,

Death Valley was submerged

by ancient seas.

Around a billion years later,

volcanic mountains drove

the seas away.

13 million years ago,

the continental crust

started stretching apart here.

And by 3 million years ago,

Death Valley was one of the

lowest points on earth.

The clue that showed

investigators what happened next

was the discovery in the valley

of a little-known

but highly valued

white crystalline rock.

>> When one thinks

of prospectors

in the Death Valley region,

one often thinks of them

hunting for gold and for silver.

But there was one mineral

that was much less glamorous,

much less sexy and exciting,

and that was borax,

but it was actually known

as the white gold of the desert.

>> In 1880, borax was a rare

but in-demand mineral used

in antiseptics and detergents.

One impoverished couple

desperately trying to make

a living in Death Valley

was Aaron and Rosie Winters.

They heard from a passing

prospector that they could make

good money from borax

if they could find it.

They learned from their fellow

prospector the then-secret

method of testing rock

for borax.

Anxious to keep potential

profits for themselves,

the couple waited until

the dead of night to perform

the test in Death Valley.

>> You burn the mineral

to see if the powder

that we have in front of us here

contains any borax.

Now, what the Winters did

is to add sulfuric acid

to borax-bearing mineral.

We'll add some alcohol.

The Winters probably used

cheap whiskey back in 1880.

And the flame should burn

hopefully a green color

if borax is there.

And as we can see,

the flame is green in color.

And in 1880, the Winters knew

that they would become wealthy

because they had borax.

>> From these humble beginnings,

a whole industry grew

in Death Valley.

It made the Winters' fortune

and also gave scientists

a priceless clue in their quest

to understand the geological

history of Death Valley,

Because borax deposits

like these can only be found

in the beds of ancient

freshwater lakes.

The sea water that once covered

this valley had long gone

a billion or more years earlier.

But the presence of borax proves

that freshwater must have

flooded into the area

when ice-age glaciers started

to melt from the surrounding

mountains around 200,000

years ago.

As the glaciers melted,

rivers flowed towards

the lowest point--Death Valley.

Gradually a vast lake spread out

across the flooded valley floor.

The valley's catchment area

was huge. Its rivers drained

more than 9,000 square miles,

an area bigger than

New Hampshire.

The water pouring in

from the surrounding mountains

leached minerals such as borax

from the rocks and deposited

them on the lake bed.

>> In a lot of the lake beds,

this mineral, borax, would

appear as kind of a white

fuzzy mineral. It was actually

called cotton ball.

>> the borax proved

that a lake existed here.

Geologists called it

Lake Manley, after one

of the pioneers,

William L. Manley, who had

named Death Valley in 1849.

But they had no evidence

to tell them its depth

and its size.

A solution to this puzzle

is revealed in this small hill

with a road cut straight

through it near the valley's

edge at a spot called

Beatty Junction.

>> It's very fortunate to have

a road cut right through

this gravel deposit.

So, in the exposure, we can see

very well rounded pebbles.

We can also see some crude

layering in the gravels.

And they're stacked in

against each other.

And we call that shingling.

>> The shape and the smoothness

of the stones tells Caskey

exactly how these pebbles

got here.

>> Yhe way they're stacked

tells us that the direction

of water flow that laid

these pebbles down like this

was from the right to the left.

So we know that this had to be

wave action. That's strong

evidence that this is

a beach environment.

>> By looking at the height

of this pebble beach

above the valley floor,

Caskey calculates the dimensions

of the lake.

>> From this beach gravel bar

that we're standing on,

the waves would have been

crashing at our feet,

and as we look south,

it's hard to imagine

a lake sitting out there

across that vast salt pan.

But Lake Manley would have

covered about 600 square miles

and it would have been about

450 feet deep.

It's odd mapping shorelines

on a really hot day

in Death Valley.

You kind of long for

the ancient days of yore,

when there were big lakes

out here. You can imagine

this was a beautiful place

full of lush vegetation.

You know, it was quite

a different place

than it is today.

>> For Caskey, the next step

is discovering why Death Valley

no longer has a lake.

And there is evidence about that

in one of its most unusual

landscapes--this twisted,

jagged field of white peaks

that's called

The Devil's Golf Course.

Even the sounds here

are mysterious.

In the silence of the desert,

there is a faint popping noise

as the relentless sun

sucks every drop of moisture

out of the parched surface.

[popping sounds]

>> The salt that we see here is

the remains of an ancient lake.

It's called Devil's Golf Course

because it's probably

the least likely surface

that you would ever want

to play golf on.

>> The surface is made up

of rough salt crystals,

popping when they expand and

contract in the searing heat,

but this salt did not

come from the sea.

Just like the borax, the salt

was leached from the rocks

when freshwater started flowing

into Death Valley

200,000 years ago.

The salt was originally

dissolved in the freshwater

Lake Manley, and Caskey

has a simple experiment to show

exactly how it ended up

on the floor of Death Valley.

>> I'll pour the water and salt

solution into this pan,

and as the water evaporates,

we should see salt forming.

And that's exactly how this

salt crust forms.

So...

it's hot enough out here today.

It should evaporate

pretty quickly.

In a fairly short amount

of time, there are some

beautiful salt crystals formed

along the edges.

That's essentially how

a salt pan forms.

When the rainwater comes in,

the salt goes into solution,

basically just like the water

that we have in this water

bottle, and from the moment

the water starts evaporating,

salt crystals start forming.

>> Today, Death Valley's

salt pans cover more

than 200 square miles,

An area 3 times the size

of Washington, D.C.

They are the remnants

of the ancient lake

that finally disappeared

2,000 years ago, when Earth's

climate began to warm up.

From then onwards,

Death Valley's temperatures

just kept on rising.

>> Death Valley is definitely

one of the hottest spots

in the world.

The record high

was 134 degrees fahrenheit,

recorded back in July 10, 1913.

And just to give you

perspective on that,

the caretaker of the Furnace

Creek Ranch, who actually

was the one doing the recordings

back then, he describes that day

as being so hot, he saw

the swallows falling dead

in flight.

>> Geologists today understand

how Death Valley's unusual

geology is responsible

for the punishing climate

that killed off its lake.

It stays so dry because there

are 3 distinct mountain ranges

between Death Valley

and the moisture carried

off of the Pacific Ocean,

over 200 miles away.

>> We have the Sierra Nevadas

to the west of us.

The storms come in from the west

laden with moisture.

As they rise up, they lose

most of that moisture

on the west side,

and each set of mountains

wicks a little more moisture

out of the clouds.

And here, with our 3 sets

of mountains in between us

and the ocean, by the time that

moisture gets to Death Valley,

there's either all gone, or we

just get a few drops of rain.

>> Almost all storms

from the coast are stopped

by the 3 mountain ranges,

each one in turn having

an effect the scientists call

a rain shadow.

>> So we are in the rain shadow

of a rain shadow

of a rain shadow and average

less than two inches a year.

>> And there is another way

that geology influences

the desert climate.

Air heated under

the cloudless sky is trapped

by the surrounding mountains.

In summer, Death Valley becomes

a deadly, dangerous furnace.

The local weather station

provides a graphic demonstration

of how quickly that heat

could have destroyed

Death Valley's lake.

Every day, Callagan checks

the rate of evaporation.

>> The summer months,

it may take 5 of these

containers here. So I'm going to

fill them up and dump them into

the pond until it brings the

water level up to the needle.

Now, our average rainfall

is barely 2 inches a year,

but the evaporation pond records

up to 150 inches of evaporation.

>> That huge discrepancy

between the amount of rainfall

and the speed of evaporation

means that a lake 12 feet deep

and 30 miles long would

evaporate in just a single year.

Lake Manley was bigger

than that, but over time,

it never stood a chance.

The scientists' studies

of Death Valley have

solved the mysteries

of its freshwater past.

Borax, discovered here

in the 1880s, proves

that Death Valley was once

filled with a freshwater lake.

Pebbles unearthed on an ancient

shoreline show the lake once

covered 600 square miles,

an area 3 times the size

of Chicago.

When the last freshwater pools

dried up here 2,000 years ago,

Death Valley started its reign

as the driest place in the U.S.,

which makes it ironic that

the investigation's next phase,

examining the valley's most

recent geological upheavals,

involves scientists studying

the awesome power

of fast-flowing water.

>> Around 100 million years ago,

Death Valley's ancient seas

gave way to exploding volcanoes

whose peaks were then

wrenched apart to create

the lowest spot in America.

From around 200,000 years ago,

the valley filled

with a freshwater lake.

But the rain shadow

of surrounding mountains

dried up the water.

For the past 2,000 years,

Death Valley has been hotter

and drier than anywhere else

in North America...

which makes it all the more

mysterious to find

Mosaic Canyon, a deep chasm

seemingly cut by water,

in this parched and arid land,

especially when there is

evidence of massive boulders

having been pushed around

like pebbles.

>> Just look at the size

of that boulder and look at

how high above my feet it is.

It's about 3 feet in diameter,

and I can't even estimate what

the weight of that thing is.

>> She may be in a desert,

but Messina knows there is

only one force that could have

lifted the boulder up so high.

>> Water brought it here

and left it here.

The force of the water

that came through here

had to have been pretty severe

in order to get that boulder

up there plastered

against the wall.

This boulder gives us evidence

about the force of the water

that comes down these canyons

during flash floods.

>> A flash flood is one

of nature's most lethal weapons.

>> If there were a flash flood

coming down this canyon,

I wouldn't have enough time

to run out of its path

because the water flows down

at an incredible velocity.

Flash floods are among

the most violent processes

on the earth.

They can carry material

the size of an S.U.V.

without any problem at all.

>> In one of the driest places

in the world, the floodwater

comes from a surprising source--

rain.

On average, Death Valley

receives just two inches of rain

a year. This is less than half

the rain that falls on New York

in a single month.

But violent summer storms

mean it can all fall

in just a single day.

The floods transform

the desert landscape

in a number of ways.

One is known as the desert

bloom, where seeds and plants

that may have lain dormant

for up to 10 years burst into

flower after a sudden rainfall.

This phenomenon might be

beautiful, but there is

another, deadlier side

to these floods,

with a human cost.

>> In 2004, there was

a flash flood that came

down Furnace Creek.

It was just this muddy slurry

that was dense enough

to pick up a vehicle

and carry it downhill,

and several people died in it.

The 2004 flash flood is small

in compason to some of

the events that we see preserved

here in the rocks.

>> Flash floods happen

all over the world,

but there's evidence here

of their particular and rare

geological effect

in Death Valley.

>> This marble is

very highly polished.

It's not scratched.

It's not gouged.

It's been polished

by very fine grained material

that comes down as part

of a flash flood.

So it's really smooth,

and it's fluted.

It's really unique.

>> To uncover how these unusual

polished walls were formed,

Messina takes a closer look

at what geologists term

the badlands.

>> I think it's called bad

because nothing will grow on it.

There's just this very loose

material out here,

and it erodes so readily that

plants can't even take root.

So this is "bad land."

>> The rock that makes up

the badlands is the dried-up

remains of the 2,000-year-old

lake bed that once submerged

Death Valley.

>> This is nothing more

than desiccated mud.

It's called mudstone because

it's slightly lithified,

meaning it's turned into rock.

>> The mudstone's minerals

are arranged in tightly packed,

flat sheets.

>> The rain can't penetrate

the mudstone, and therefore,

the rain picks up a lot of the

particles and carries

them downhill.

>> These particles are the key

to the canyon's smooth,

polished walls.

>> It flows through here

so laden with sediment

that it causes a lot

of polishing and incision.

So every time a flash flood

comes through, this canyon

gets deeper, the walls

get higher, and the rock

gets more polished.

>> The sediment-laden floods

can carve into Death Valley's

rocks with tremendous

speed and force.

These canyons have been

gouged out where the rocks here

have been fractured

and weakened by the continuous

stretching the valley

is undergoing.

>> This is up-front,

in-your-face geology

happening right here.

Death Valley is dynamic.

This is a place where things are

happening in a human lifespan.

>> In this arid desert,

yhe investigation has identified

water as the latest factor

in Death Valley's continuing

geological evolution.

The giant boulders plastered

high on the canyon walls

illustrate the power

of flash flooding in the desert.

The smooth walls of mosaic

canyon show how the dried mud

from an ancient lake still

affects how Death Valley

is being shaped to this day.

And yet some mysteries

remain unsolved, including one

of the world's most intriguing

geological riddles--the rocks

that seem to walk by themselves,

moving thousands of feet across

the floor of Death Valley.

>> Over 1.2 billion years,

Death Valley has been

transformed from a watery

landscape to a barren desert.

But even though geologists

now understand the processes

that have shaped this

extraordinary region, there are

still mysteries to be solved.

And there is no part

of Death Valley more mysterious

than an area known

as the Racetrack.

This parched, cracked lake basin

just 2 1/2 miles long

and a mile wide

is the setting for one

of Death Valley's most

intriguing geological puzzles--

its sliding stones.

>> I love this place

because it's odd.

I could come here

a hundred more times,

and every time there will be

something different,

something I didn't see.

>> Stretching behind these rocks

are long grooved trails

in the earth.

It is clear that they are tracks

left behind as the rocks move

across the valley floor.

The puzzle is to work out

how the rocks can slide uphill

against this slightly tilted

surface.

These are no mere pebbles.

Some of these rocks

are over 700 pounds.

And some of the trails

are nearly 3,000 feet long.

The phenomenon was first

recorded here by scientists

some 100 years ago, and yet,

in this remote location,

no one has ever seen

the rocks moving.

Messina has been tracking

the movement of each

individual rock on the Racetrack

since 1996. Her gps readings

are accurate to within

a single inch.

>> Geology is really nothing

more than detective work.

And rather than looking

for evidence of things

that took place a long time ago,

what I really like about

working on the Racetrack

is you are looking at things

that are happening right now.

It's an ongoing process.

>> Her first clue is the surface

on which the rocks slide.

>> If I try to move my hand

over it, I could probably

file my nails right now.

However, after it rains,

there's so much clay

in the lake-bed sediments

that it gets slick.

It's almost like teflon.

You wouldn't need very much

force to set even a very large

rock into motion, just because

the friction on the surface

is almost nil.

>> But water alone isn't enough

to make these rocks move.

Messina has identified

a second factor at work.

>> You can have rain,

but if you don't have wind

a couple of days later,

I don't think these rocks

are going anywhere.

>> The Racetrack is

a natural wind tunnel.

The wind funnels into the valley

from the south.

Close to the ground,

the winds can exceed hurricane

strength, reaching speeds

of over 90 miles per hour,

enough to push the rocks

into action.

>> If you have wind

and there is no friction,

all you'd need to do

is hit a rock with your finger

like that, and it would go

into motion.

>> When all these elements

are in place, the rocks can

Begin their mysterious journey.

[thunder]

>> Since no one has ever seen

the rocks in motion, we can

only guess how fast they go.

But based on some of

the evidence that I've seen,

these rocks aren't

inching along, by any means.

And the best estimate we have

is about 3 to 4 miles an hour.

So a nice, brisk walk.

>> But until this phenomenon

is witnessed, the mystery

of Death Valley's sliding rocks

will remain.

>> I hope that this mystery

isn't solved. It's what

keeps me interested, and I think

it's what keeps a lot

of people interested.

>> Geologists studying

Death Valley have figured out

its extraordinary geological

evolution.

Stromatolite fossils show

that this area was once

covered by seas.

Turtleback rocks prove that

the land was stretched apart

by tectonic forces,

dropping the valley floor down

to the lowest point in America.

Pebbles at Beatty Junction

prove that Death Valley was once

covered with a freshwater lake.

And the smooth, polished walls

of Mosaic Canyon show that water

is still at the heart of

Death Valley's modern evolution.

Death Valley remains

one of the most extreme

geological wonders on earth,

and it's still evolving.

Its valley floor is being

constantly pushed apart

by forces deep within the earth.

This means that the crust here

will continue to stretch

and thin. One day,

tens of millions of years

into the future,

Death Valley could be

separated by the sea

from the rest of the U.S.

Today, Death Valley continues

to sink at a steady rate

of 1/10th of an inch a year,

while its surface continues

to be sculpted by water,

living proof that the Earth

is never at rest.