What if a single, you know, relatively short
river in the south of Spain could act as a literal
time machine? Oh, I love that framing. Right.
And I don't mean a metaphorical sit on the bank
and just kind of think about the past kind of
time machine. Sure, sure. I mean, a physical
record of the Earth tearing itself open. Yeah,
literally. A journey taking you from, like, Nine
million year old geological escape rooms straight
through to five thousand year old cliffside fortresses
built by some of Europe's earliest settlers.
Welcome to the deep dive. We're so glad you're
here. It really is quite the the intricate journey
we are mapping out today. It totally is. And
today's mission is pulling apart a brilliantly
dense Wikipedia article detailing the Cassin
River. The Cassin River. Yeah. This is a waterway
in Andalusia, Spain, down in the province of
Grenada. But we aren't just doing a rote geography
lesson today. No, definitely not. The goal is
to truly understand the underlying mechanics
of how water acts as the ultimate sculptor, you
know, of both the earth and human history. Right.
Because when you look at a river today, standing
on its banks, it looks, well, permanent. Yeah,
it really does. It gives the illusion that it
has always been there, just quietly flowing in
that exact path. But the Cason River's story...
is fundamentally one of dramatic violent change.
It's kind of crazy when you dig into it. What's
fascinating here is the sheer scale of the river's
journey from being trapped in a basin to eventually
carving out a sanctuary for early humans. To
understand the beautiful, rugged canyon environment
that exists right now, we actually have to start
our story at a time when this river couldn't
go anywhere at all. Nowhere at all? Right. It
was essentially trapped. OK, let's untack this.
We have to go way back. Way back. We are looking
at the Late Tortonian and the Middle and Late
Tyrolean eras. Geologically speaking, we are
talking roughly 9 .0 to 5 .3 million years ago.
A massive stretch of time. Yeah. And during this
massive stretch of time, the entire Granada Basin
was what Geologists classify as an endorheic
basin. That is the the crucial foundational term
for this whole narrative endorheic And the best
way I can think to visualize an Andorheic basin
for you is to imagine a giant, regional -sized
bathtub. A bathtub, right. But the drain has
been completely plugged up with a rubber stopper.
You had rivers flowing in from the eastern mountains
and rivers flowing in from the southwest, all
pouring into the central lake in the basin. Pouring
in, but not leaving. Exactly. There was absolutely
no exit. Well, the bathtub visual works perfectly
for the mechanics. scale that up to a terrifying
degree. Oh, for sure. Imagine if the water evaporating
from that closed tub left behind thousands of
tons of heavy, mineral -rich sludge every single
year. Yeah, that's a lot of sludge. In a closed
system like that, the water has nowhere to flow
out to the sea. It evaporates, sure, but all
the sand, gravel, the loose clays. The heavy
stuff. Right. The immense volume of sediment
that those rivers carry down from the surrounding
mountains, it all just settles at the bottom.
Millions of years of rivers acting like, I don't
know, delivery trucks, just dumping earth into
this locked room, slowly filling it up to the
brim. It's a landscape defined entirely by deposition.
It is purely collecting. Just piling up. There
is no carved terrain. Just an ever thickening
layer of flat heavy sediment pressing down on
the earth, but the earth rarely stays static
forever, you know Eventually, it decides it's
time for a breakout. A massive structural one.
As we move out of those eras and into the Pliocene
and eventually the earliest Pleistocene eras,
the tectonic plunning of the entire Iberian region
radically shifts. The Earth is actually moving.
Exactly. The Earth's crust is moving. Mountains
are pushing up. And because of this regional
tilting, the western part of this basin started
being drained by the Paleo -Casene River system.
OK. It started pushing north and eventually hooking
west. But the real game -changer, the mechanism
that broke the bathtub, was the Janelle River.
When I was looking into the Janelle River's role
in this, I was just stunned by the sheer physics
of it. Oh, it's wild. The Janelle River physically
changed its course to flow west, linked up with
the Paleo -Cassine system, and suddenly the entire
basin flipped from being endorheic to completely
exorheic. Exorheic. meaning it drains out. Right.
The drain in the bathtub was violently unplugged.
Well, the sheer scale of consequence from that
single hydrogeological event is staggering. It
flipped a switch in the Earth's mechanics for
the entire region. It totally did. Think about
the energy involved. For millions of years, the
Granada Basin had been passively collecting sediments.
But once that river system broke out and found
a downward path to the sea, the flowing water
gained incredible kinetic power. It's moving
fast now. Very fast. The basin went from collecting
sediments to aggressively eroding them. So the
river stops being a delivery truck dropping off
dirt and suddenly becomes a massive excavator
digging it all back up. That's a great way to
put it. And erosion isn't just water lightly
touching rock. It's water carrying abrasive sand
and gravel, acting like liquid sandpaper at high
speed. Wow! Liquid sandpaper! Yeah. That shift
from deposition to aggressive erosion is what
sets the stage for the dramatic landscapes that
define the region today. The water was now slicing
straight down through millions of years of that
soft, accumulated sediment. So this river spends
millions of years acting like a buzzsaw, creating
these massive steep drops. Exactly. Geologically,
that is a violent process, but biologically it
creates a fortress. Which brings us to the present
-day geography and the river's most spectacular
feature. Yes. The word tajos refers to these
sheer, steep cuts or gorges. And the scale of
this specific gorge is just breathtaking. Let's
trace the water from the very top, because the
contrast between where it starts and where it
ends up is amazing. It really is night and day.
The Cansin River originates high up, over a thousand
meters above sea level in the Sierra de la Almejada.
The water filters down from these high -altitude
aquifers made of limestone, shale, and quartzite.
Which is an important detail. Limestone and quartzite
act almost like giant natural sponges. Oh, really?
Yeah, they hold the water and release it slowly
and consistently. That's why the river can flow
year -round and continue its work of erosion
rather than just flashing and drying up. That
makes sense. It bursts out into the world through
these wilderness springs with beautifully evocative
names. You have Agujerio Caliente, Manticana
Las Gondrinas. Very poetic. They sound perfectly
serene and they run through these pristine, high
altitude wilderness areas. The runoff from the
north face of those mountains eventually collects
in what is now the Los Bermejales Reservoir.
But once the water leaves that reservoir and
heads north, the serene sanctuary vibe abruptly
ends. It's over. Completely. The underlying geology
changes and the terrain gets intense. The river
hits the Tajos de los Bremahalas. Wait, so when
we say the earth here is made of quaternary sandstones,
clays, and conglomerates, what kind of rock are
we actually dealing with? Good question. Is this
like the crumbly stuff left over from the bathtub
era? That is exactly what it is. Because these
were loosely packed sediments from when the basin
was a giant lake, they lack the solid heat -forged
crystalline structure of older rocks like granite.
So they're soft. Very. They are highly susceptible
to rapid water erosion. So when the newly energized
river hit this soft quaternary layer, it didn't
just casually flow over it. It carved it up.
It dug straight down, almost like a knife. through
an incredibly dense layer cake. Wow. It created
this incredibly narrow canyon with sudden, sheer
100 -meter drops. If you were standing at the
edge of the Tajos today, you'd be looking down
a 330 -foot vertical plunge of raw, exposed clay
and sandstone. It is a harsh, raw, deeply eroded
environment. And apparently people hike this.
They do. There is a walking trail through the
gorge, but it's officially classified as a difficult
route. You aren't just taking a stroll, you are
dealing with sections of hanging bridges, literal
metal ladders bolted directly into the rock face.
Not for the think of heart. No, and there are
support ropes you have to grip just to navigate
the narrowest cuts. Oh, and there is a hilarious
historical quirk on this trail. Oh, I know what
you're gonna say. You are hiking through this
treacherous prehistoric gorge, gripping a rope
for dear life, and you arrive at a majestic landmark
known as the Roman Bridge, which, as it turns
out, was actually built in the 1940s. A slight
branding error by the local tourism board, perhaps.
Just a bit. I mean, missing the fall of the Roman
Empire by roughly 1 ,500 years is quite the stretch.
It is. But 1940s concrete bridge doesn't have
the same romantic ring to it when you're marketing
a rugged adventure trail. It really doesn't.
but the human infrastructure is really just a
footnote here. What is truly remarkable about
this gorge is the natural adaptation happening
on those sheer walls. The wildlife. Yes. This
deep, harsh canyon with its 100 -meter vertical
drop somehow became a thriving, heavily protected
ecosystem. I mean, how does anything survive
on a sheer, crumbly clay cliff? There's no ground
to stand on. By entirely utilizing the verticality.
The canyon walls offer perfect protection from
land -based predators that simply cannot navigate
the drops. You say they'd fall. Exactly. It creates
an aerodynamic haven. You have an incredible
array of bird colonies that make their home right
on the sheer walls, utilizing the updrafts created
by the narrow gorge. Oh, wow. You have raptors
soaring through the corridor, common kestrels,
and the Eurasian eagle owl. scientifically known
as bubo bubo. The bubo bubo. It thrives here
because it can nest in the inaccessible crags
high up and use the narrow river corridor below
as a concentrated hunting ground. That's brilliant.
And alongside the massive raptors you have colonies
of western jackdaws, rock doves, bee eaters,
barn swallows, and Eurasian crag martens. It
is a veritable high -rise of avian life. Just
a wall of birds. Pretty much. Yeah. But it's
not just birds taking advantage of the verticality.
The gorge is also navigated by the southeastern
Spanish Ivex. Wild mountain goats just casually
defying gravity on a 330 -foot drop. It's amazing
to watch. They have highly specialized cloven
hooves with rubbery pads that allow them to grip
the almost vertical clay and sandstone walls.
Gripping clay. Yeah, they use the sheer drops
as a shield against predators. It paints such
a vivid, almost contradictory picture. You have
this river that spent millennia violently tearing
the earth open, destroying the flat landscape.
But in doing so, it accidentally carved out this
perfect fortified sanctuary for an entire vertical
biome. Exactly. And that concept of a fortified
sanctuary brings us to the human element of the
Cassian River story. Because wildlife weren't
the only ones to look at those towering, unscalable
walls and realize the strategic value of an inaccessible
fortress. Here's where it gets really interesting.
We're zooming forward from millions of years
ago to about 5 ,000 years ago. The Neolithic
era. The early humans. Early humans look at the
Tajos de los Bermejales with its sheer cliffs
and its flowing water, and they decide to move
right in. Literally into the walls of the canyon.
Yes. They lived sheltering under the overhanging
walls. And to me, this isn't just seeking shelter.
This is a prehistoric high -rise apartment complex.
That's a really good analogy. They didn't just
find deep caves to hide in. They found shallow
natural cavities and overhangs in the canyon
walls. And they actively built physical dry stone
walls across the front to enclose them, making
them into secure elevated homes. They were engineering
their environment. And think about the brilliant
strategy of it. You live high up in an enclosed
rock cavity where no rival group or large predator
can easily reach you. Right. Because of the drop.
But you have this conveyor belt of resources.
Fresh water, fish, hunting grounds flowing right
past you at the bottom of what is essentially
a massive natural fortress moat. And the wild
thing is, you can still see the traces of some
of these built walls today. You can, but this
raises an important question about the physical
logistics of living there. It's a detail that
is easy to gloss over if you aren't speaking
about the scale of geological time. Those Neolithic
dwellings, those high -rise apartments. Today,
they sit about 10 meters above the present river
level. 10 meters. That's like over 30 feet in
the air. Over 30 feet. Lugging water and supplies
up a 30 -foot sheer cliff every single day sounds
exhausting, even with ladders. It would be. If
we connect this to the bigger picture of the
river's geological history, that constant relentless
erosion we talked about earlier, we realize the
canyon floor wasn't 30 feet down 5 ,000 years
ago. Wait, are you saying the physical river
was higher up the cliff face? Yes. The river
was physically much closer to those dwellings
when the Neolithic people actually lived there.
Oh, wow. They absolutely built their homes slightly
elevated for defensive reasons, using stairways
and ladders to reach them, keeping themselves
safe. But over the last five millennia, the Cassine
River just kept doing what it does. Which is
digging. It kept digging. That is a mind -bending
concept. So the human history stayed bolted to
the wall, but the earth itself moved. The river
literally dropped the floor out from under their
history. It excavated roughly 30 feet of solid
quaternary sandstone and clay over 5 ,000 years
while those abandoned walls just sat up there
watching the water get further and further away.
That's so much rock. If you do the math on that,
it means the river has been carving away about
two millimeters of solid rock every single year
since the Neolithic era. Two millimeters a year.
It is the perfect illustration of water as a
slow, unstoppable sculptor. And because the river
was the center of their lives and physically
closer to their homes, their artifacts naturally
found their way into the water. They did. Which
brings us to perhaps the most significant historical
discovery in this entire area. The Cassine Pot.
or the Olla de Cacín as it is known in Spanish.
It's an ancient clay vessel that was found right
down there in the riverbed. The water had essentially
swallowed it and held onto it for millennia and
preserved it. It's such a significant find that
it was carefully extracted from the gorge and
is now preserved in the National Archaeological
Museum in Madrid. Its significance goes far beyond
simply being an old clay pot. The Oia de Cassin
is a specific type of artifact known as cardium
pottery. Okay. And it represents the most southern
example of this specific pottery found in all
of Europe. Which begs the question, What exactly
makes cardium pottery so special to archaeologists?
Why does this one pot in Madrid matter so much
to the timeline of human history? Well, cardium
pottery is named after the Cerastoderma edul,
which is a type of marine cockle shell. A seashell?
Yes, a seashell. During the Neolithic period,
a specific culture of early humans would press
these cockle shells into the wet clay of their
pottery to create distinct decorative imprints
before firing it. It's often called impressed
wear. But a cockle shell is a marine shell. That's
a coastal resource. The Cassine River Gorge is
tucked away inland deep in the rugged mountains
of Andalusia. Exactly the point. This pottery
technique originated along the coastlines of
the Mediterranean. It tracks the maritime expansion
of early farming cultures. Oh, I see. So when
archaeologists find a pot stamped with coastal
shells buried deep inside an inland river gorge,
it becomes a massive archaeological marker. Proof
of movement. Right. It proves that these Neolithic
people didn't just stay on the beaches. They
migrated inland, navigating these treacherous
mountain passes. Or they established complex,
long -distance trade networks with coastal groups.
That is incredible. These people pushed inland.
found this violently carved gorge, recognized
it as a natural fortress, built their ladders,
set up their high rises, and brought their distinct
coastal pottery traditions with them. And then
they left. And then they left. And the river
just kept cutting deeper and deeper into the
earth, preserving the traces of their homes high
up on the canyon walls while burying their pottery
deep in the riverbed. It truly functions as a
time machine. The geology and the human anthropology
are completely intertwined. So what does this
all mean? We started this deep dive looking at
the documentation of a river in Andalusia that
flows north to join the Genual River. On paper,
it is just another geographical line on a map.
Sure. But when you really look at the mechanics
of it... The Cassine River is a living, flowing
record of the Earth's sheer power and consequence.
It is the story of an ancient, trapped lake finally
breaking its boundaries. Unplugging the bathtub.
Exactly. It's the story of water violently carving
a 100 meter gorge out of soft clay, dropping
the floor millimeter by millimeter. And it's
the story of a defensive sanctuary that kept
ancient Europeans safe five thousand years ago,
holding on to their secrets until we were ready
to find them. It serves as a powerful reminder
for all of us, the landscapes you drive past,
the wilderness trails you might hike, even the
difficult ones with ironically named 1940s concrete
bridges, they are not static painted backdrops.
They are active ongoing processes. They are the
result of millions of years of hidden geological
drama and ancient human adaptation. The earth
is still moving. The tectonic plates are still
shifting and the rivers are absolutely still
digging. And that leaves us with one final thought
for you to take away. Think about that constant
relentless digging. It never stops. The water
is still rushing down from the high aquifers.
It is still carving through the rock. If the
Cassian River has eroded the canyon floor 10
entire meters deeper since those Neolithic people
lived there just five thousand years ago, what
is it carving into right now? That's a great
question. Upstream, the river cuts through the
Alpujarid reliefs. These are complex, much older
mountain structures full of folded rock and and
hidden history. What undiscovered artifacts,
what pieces of forgotten human or geological
history are currently being washed down from
those high reliefs today? We don't know. Right
now, entirely hidden beneath the flowing water,
just tumbling along the bottom of the gorge,
waiting to be found by whoever wanders the Tajos
thousands of years from now. The time machine
is still running, and it's still collecting data.
Thanks for taking the deep dive with us today.