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,
every place on Earth does have its own unique geological tale that’s just waiting to be told.
Hope you enjoyed this natural history tour of LA and the surrounding areas.
Let us know in the comments where you want us to go next! I'll pack my bags.
Thanks to this month’s angelic Eontologists:
Annie & Eric Higgins, Chase Archambault, Colton,
Jake Hart, John Davison Ng, Yanshuo Li, and Melanie Lam Carnevale.
By becoming an Eonite at patreon.com/eons
you can get fun perks like submitting a joke for me to read, like this one from Philip
What did the paleontologist say when he had to get back to work?
I’d love to stay, but I’ve got to split!
I mean I guess? If you're working in shales and sediments and sure.
And as always thanks for joining me in the Adam Lowe studio. Subscribe at youtube.com/eons
for more journeys in deep time!
We are on our way to hopefully find the San Andreas fault road cut. Let's go. You're
going to see where North American Plate and the Pacific Plate are literally just like [noises]
Alright, please be the fault. Please be it.
Is that it right there?
No [laughs]
Oh no! That was it! [bleep] It was the other side. The fault.
It's so pretty.
I kinda got something. I just stuck my pits in Farhan's face I'm sorry. [laughs]
I gotta split? Liek do you split open rocks and...