It’s hard to imagine a more unnatural environment   than the city of Los Angeles – a sprawling  metropolis of concrete, glass, and people.

It’s a testament to the human ability to  reshape a landscape beyond recognition - almost.

See, despite the profound changes  we’ve made here in recent history,   the epic saga of this area’s natural history is   still visible - and even striking - if  you know where and how to look for it.

This is a story about the ancient,   deeply interconnected forces and  events that have shaped this region.

It’s a journey that begins millions of years  ago with the formation of the San Andreas fault   and ends with the creation of the  iconic tar pits at Rancho La Brea,   an active dig site located in the center of LA.

Because, as you’re about to see,  even in the biggest and most heavily   developed urban environments, natural history  is all around us, just waiting to be explored.

This episode is going to be a little different.

We’re leaving the Eons studio to experience the  geology and paleontology of a place first-hand.

Consider us your natural history tour guides –  and we’d love it if you came along for the ride.

Michelle, this is where our journey begins.

Welcome to California!

I can't think of anyone better to  reveal the natural history of Los   Angeles than my friend and colleague and  professor of geology, Michelle Barboza-Ramirez Our journey begins in Vasquez Rocks Natural  Area Park, about 70 km north of downtown LA.

If its towering, tilted rock formations seem  strangely familiar, there’s probably a good   reason for that.

This area’s geology has formed  the backdrop of hundreds of movies and TV series.

But tens of millions of years before  becoming the site of Hollywood blockbusters,   this area experienced its ‘biggest  hit’ of all - the collision of the   North American and Pacific plates,  forming the San Andreas fault.

San Andreas Fault plays a very big part  in why these rocks look the way they do.

So take a look behind you.

These  rocks are tilted, like hella titled.

And if you didn't know anything about geology,   you'd see them be like "Wow , that's so weird  that these rocks formed, like, sideways."

Well, I will tell you they did  not form sideways, they formed   horizontally.

It's actually one of the laws of  stratigraphy if we want to get geology nerdy.

And it's called the "law  of original horizontality" Which, horizontal means flat.

And original means  that's how it used to be.

All rocks form flat.

Why?

Um.

Gravity.

Ok.

If sediment is on an incline,   it's going to keep rolling down.

It  rolls down hill.

Gravity is pulling it.

Eventually it's going to land, let's say,   on the basin of my hand.

When  it lands here, it's stays flat.

Now, if all of this sediment was  already flat and like welded together,   and then the floor started moving,  it's gonna be stuck together right?

It can no longer have individual  pieces that are falling off.

So if you ever see rocks that are tilted, you  know that they had to have formed flat first   and then solidfied before  something pushed them up sideways.

And that's where the fault comes in.

That's where the fault comes in.

The fault itself is literally   where two tectonic plates are meeting.

I mean, we say Californians live on  like a different plain of existence,   where on a different tectonic plate, Blake!

[laughs] Literally.

The rest of North America is on  the North American Plate.

We,   right now, our butts, are on the Pacific Plate.

We're not on the same tectonic plate  as the rest of the United States.

So the San Andreas Fault is where  the North American Plate starts   so the North American Plate, the Pacific Plate are   touching like puzzle pieces and the reason we call  it a Transform Boundary is because instead of,   like, pushing up against each other or moving away  from each other, they are just kinda sliding past.

But the fault itself is not necessarily what's  pushing it.

It's more like the after effects   of the fault kinda like deforming  and pushing everything else around To say that the San Andreas Fault like  directly came and pushed these rocks up   is incorrect.

But did the fact that it exists  and it's pushing everything else around and   other little faults are coming off of it.

It  all ties back there, baby.

Plate tectonics.

A whole series of faults.

That's.

That's like my personality.

[laughs] But this is only where our story starts.

The  formation of the San Andreas fault really sets   the stage for what’s to come…because tectonic  plates don’t just bump into each other and stop.

Moving southwest towards the Pacific  Ocean, we run into another consequence   of the collision that created the San  Andreas fault: the Santa Monica mountains.

This range is a panoramic feature of the Los  Angeles landscape, stretching around 80 km   in length and peaking at just under 950 meters  high.

And Michelle made me climb a lot of that.

We're going on on what Michelle calls "A hike" We're not out of breath at all.

But despite being an iconic part  of the city’s skyline today,   the story of these mountains began on the seabed.

Over millions of years, the ongoing pressure of  the tectonic plates along the San Andreas fault   triggered volcanic activity and  pushed the mountains skyward.

Ok i have questions, hold on.

[Laughs] I'm fine by the way.

Thanks for asking.

Ok so we were just at Vasquez Rocks and now  you're making me climb the Santa Monica Mountains Making?

You chose this.

You love this!

[Laughs] So we're in the Santa Monica Mountains Recreation  Area, which is part of the National Parks Service And we have, I want to say, over  2300 fossil sites in these mountains.

Wow, really?

Yes.

And a majority of them are.

Marine life, actually.

That was going to be my guess.

So, remember, we were talking about  the underwater volcanoes and all of   this sediment that we're standing  on for the most part is marine.

The reason that it's now so high is because again  part of the fact that the San Andreas has been   pushing things around, moving things up.

Tectonics  plates and continental collisions and all that.

And the immense pressure released  along the San Andreas fault   didn't just change the height of the  mountains, but their direction, too.

These mountains are part of what  we call the Transverse Ranges.

And so, most of the mountains in  California, let's say that this is   the coast.

These are the mountains.

Like  the Sierra Nevada, they run north-south.

Right.

They run parallel to the coast.

But we are in the Transverse Ranges which  are actually more like almost east-west.

So they are transecting the state.

They are the Transverse Ranges.

I would have called them the  Sideways Mountains.

But go on.

That totally works as well but we're  going to sound all fancy and science-y.

So the Tranverse Ranges.

And the reason  that they are looking like this is because   the San Andreas Fault actually grabbed Baha  California, smashed it into Southern California.

And that started dragging the mountains  and rotating them like 120 degrees.

So while these mountains may seem like a  permanent, immovable feature of the landscape,   they’re actually /far/ more dynamic than that.

Over millions of years, they’ve been  squeezed up, folded, and pivoted by the   complex tectonic activity beneath them  - a process that still continues today.

The geological journey of the Santa Monica  Mountains didn’t end with their uplift   and rotation by tectonic forces.

Throughout the Pleistocene epoch,   erosion by rivers and streams carried sediment  from the mountain range down into the LA basin.

And some of this sediment has been deposited   in just the right place at just the right time  to help create a truly spectacular fossil site   in what’s now the center of  the city: the La Brea Tar Pits.

So we were at Vasquez Rocks and then we were  at the Santa Monica Mountains and now we are- Both beautiful and exhausting.

And now we're in the more exhuasting traffic  that took us to get to downtown LA.

Ta da!

But we're also surrounded by fossils.

Or should I say on top of fossils.

There are fossils everywhere.

There are seeps in the parking lot,   there are pits all over this area.

The area is famous for the sticky asphalt  - which by the way is not tar - that’s been   bubbling to the surface for  the last 50,000 years or so.

This black goo is produced deep underground  where temperatures of 75 degrees Celsius or more   transform organic material into petroleum.

Over time, it seeps to the surface  through faults, forming pools of thick,   viscous asphalt on the ground.

Which  I thought was very fun to play with.

So this is not construction material that was  left over.

This is the tar, the asphalt.

The   asphalt that like, you know, mastodons,  mammoths, saber tooth cats go trapped in.

And we've been talking about  how it's not a pit, right?

Like,   this is not a lake that you fall into.

And these things are all over.

All over.

Most of the seeps are like, a couple inches   deep.

And they can be pretty easily covered.

Like  imagine you have some grasses growing around it.

Not these imported grasses but our  California native grasses.

So you could   be walking through and not even realize  that there's a tar seep and get stuck.

This is really fun by the way.

It's very satifying.

[Laughs] I could probably do this all day.

And it  smells like someone is paving a parking a lot.

Exactly right Although if you were living in the  Pleistocene, it smells like death.

From the Late Pleistocene epoch to the  modern-day, these hazardous asphalt seeps   have trapped countless animals, big and  small, that wandered in and got stuck.

Because I think of it as being like quicksand.

Like, an animal walks into it and  they just sink all the way into it.

Yeah there's not that much to sink.

It's  more like super glue.

Where it's like   pretty hard to get out.

And like, imagine you're walking on all fours.

You're trying to pull one arm out,  your weight is going into your back   leg.

So your back legs are sinking down.

So they you start to pull your back legs.

Now you're in trouble.

You know you're   just actually pushing yourself deeper  and deeper into the tar or the seep.

Or like let's say you're only caught for a  little bit and a dire wolf comes up behind you   and he's like, this is my ime to strike.

I've  got like just enough time to get you out.

And   then that gets stuck and then a vulture comes  to eat the dire wolf and it's just circle.

A circle of death.

A circle of death, right.

It's the circle of death!

Where we've just got bones  and bones and bones piling up.

Slowly, these poor critters were  buried in the asphalt.

Over time,   it mixed with eroded sediment  carried down from the mountains,   hardening and helping to preserve their  remains and protect them from the elements.

But where are we, right?

We are  down here in the LA basin.

The   Santa Monica Mountains are  like two miles from here.

Ok.

So we're not at an angle.

We're on the floor.

So all of that stuff that was coming down off   of the mountains was essentially covering and  burying the fossils that were trapped in this tar.

So you have tar seeps, you have  an organism.

Ugh, they're dead.

They're getting nice and covered by  the sediment that's covering them,   right?

So that's part of what's preserving  them.

They're not going to get scanvenged.

They're not going to get eroded.

They're  not going to get rained on and dissipated.

This is again like tens of thousands of  years of fossils collecting overtime.

And for over a hundred years, scientists  have been excavating these deposits,   unearthing a truly breathtaking  array of fossils that   have given us an unparalleled glimpse  into LA’s ancient biodiversity… And what's really interesting is  like, of course, when we first started   excavating here, they're like "wow,  a mastodon", "wow, a ground sloth",   "wow, a dire wolf".

Like all these big,  we call them charasmatic megafauna.

But as the years have gone by, the focus  of what we're researching here has changed.

We've been talking about animals  this whole time, right?

Like,   oh "we have a sabertooth", "oh, we have a  lizard" but like we also get plant material,   we get insects.

Again, we're able to  like reconstruct the entire ecosystem.

Not just there was a mammoth here but there was a  mammoth and he was eating this kind of plant and   this bug was eating that kind of plant and like  the whole food chain we're able to learn about.

So, asphalt is important for  preservation and also fun to play with.

And fun to play with.

As long  as you don't get stuck in it.

With supervision.

I think you're the supervisor.

Oh that's a lot of pressure.

[laughs] I wonder what's in here?

While Los Angeles today is a thoroughly  modern, human-made environment,   our journey through its natural landscape tells  a story that stretches back into deep time.

From the massive collision of tectonic  plates tens of millions of years ago that   eventually led to the tar-stained bones of  ice age giants buried under the city today,   the legacy of LA’s natural history is  just as epic as any Hollywood blockbuster.

And LA is far from alone.

While not every city sits on top of a major fault  zone or has an active dig site at its heart,