The Columbia River Gorge.
A wonderful place for many things.
Sure, sure, it’s windy out here and there’s
scenery, but there’s also incredible geology.
So many different kinds of things to look
at that prompt so many questions.
How long has the gorge been around?
How did it form?
Has the Columbia River always cut through
the Cascades to the ocean?
The rock layers in the walls of the Columbia
Gorge.
What kind of rock?
Where did the rock come from?
And why are the layers flat in some places
and titled in others?
What does the tilting tell us about the history
here?
Where’s the Bridge of the Gods?
That sounds like a cool place.
How ‘bout Celilo Falls?
Why are there so many waterfalls in the deepest
part of the gorge?
What about Beacon Rock?
Or the old scenic Columbia River Highway?
And I get this one a lot: The Ice Age floods?
That many people now know about coming from
Montana.
Did those Ice Age floods create the Columbia
River Gorge?
Blast a whole through the Cascade Range on
the way to the Pacific Ocean.
There’s so much to study out here.
Let’s get busy, question by question, and
figure this stuff out.
The Columbia River and its tributaries have
drained a large section of North America for
millions of years.
Where the river cuts through Cascade Range?
That’s the Columbia River Gorge.
The state line between Washington and Oregon.
How long has the gorge been here?
How did it form?
It’s the only passage through the mighty
Cascades.
You might be scratching your head thinking
of ways that the river could break through
the mountains, but actually, the river is
older than the mountains.
The Cascade Range is not just a pile of lavas.
Plate tectonic uplift formed the Cascades
that we know today.
3000 feet of uplift in the last 3 million
years.
Uplift during the Ice Age.
But the Columbia River has had a much longer
history in this region.
Starting 17 million years ago, the Columbia
River Basalts flooded the inland Pacific Northwest
with hundreds of thick lava flows that came
from deep cracks in the crust.
Up to 200 miles east of the Columbia River
Gorge.
Lavas that have nothing to do with the Cascade
volcanoes.
Back then, there was an ancient Columbia River
Valley 60 miles wide.
Kind of like today’s Willamette Valley in
western Oregon.
And the Cascades in those days were low.
A modest upland with occasional volcanic cones.
The Columbia River Basalts used this early
valley through the low Cascades to get all
the way to the Pacific Ocean.
We know this by carefully studying the lava
bedrock in the walls of the Gorge.
Part of a wide swath of mostly Columbia River
Basalt layers found through this stretch of
the Cascades.
The thicknesses of individual lavas are remarkably
constant from Idaho to the Oregon coast, which
means they were flowing over a landscape that
was pretty much flat.
No major Cascades at the time.
No big gorge.
But today in the heart of the Gorge, the Columbia
River Basalts are thousands of feet above
the river.
Why is this?
What happened?
Plate tectonic uplift.
An uplift that created the modern Cascades.
Remember, 3000 feet of uplift in the last
3 million years.
And the Columbia River cutting against the
uplift made the gorge that we know today.
The regional arching of the bedrock layers
was so extreme that we have a rare glimpse
at the rock layers below the basalts.
Deep in the Casades, the Eagle Creek Formation
is exposed, hundreds of feet of volcanic mudflows,
lahars, pieces of petrified wood and volcanic
blocks from from eruptions 20 to 30 million
years ago.
So the Columbia River Gorge that we know and
love is geologically pretty young, cut in
response to an Ice Age uplift episode.
And that means the dramatic vegetation changes
through the gorge, created by a rainshadow
effect, is also a recent development.
Have you driven through the gorge lately?
There’s a pretty amazing change isn’t
there from one end of the gorge to the other?
It’s certainly not all like desert stuff
that we have in eastern Washington.
You drive the gorge from west to east and
you experience a change of 100 inches of precipitation
down to 10 inches annually.
In 80 miles!
A wet set of plants down to desert plants.
With windsurfing and kitesurfing in the transition
between the two extremes.
All created by tectonic uplift.
The Columbia River itself had different courses
in the broad valley it followed through the
old, low Cascades.
There are very clear snapshots in time to
confirm this.
One of the Columbia River Basalt lavas, the
Priest Rapids flow, was liquid and hot when
it came out of deep cracks in Idaho 15.2 million
years ago.
The flow developed great columns in eastern
Washington where the land was completely flat
back in the day.
But as the lava approached the low Cascades,
the lava found a river valley with an ancient
Columbia River in it.
Like filling a mold, the lava funneled into
the valley and eventually hardened into basalt.
At The Dalles, the Priest Rapids flow is mostly
pillow lavas as the lava battled water in
the channel.
Lava versus water is always dramatic, like
in Hawaii today.
Long after the lava hardened, the old valley
walls weathered away, and the Priest Rapids
basalt shows us precisely where the Columbia
River flowed exactly 15.2 million years ago.
And the best place to see this intracanyon
flow?
Crown Point!
The Vista House sits on top of 600 feet of
a Priest Rapids lava flow that once upon a
time flowed through an ancient Columbia River
Valley.
Each lava has a unique set of minerals and
isotopes, a chemical fingerprint used by geologists
to follow the flows across the Northwest.
Other lavas show different snapshots in time
where the Columbia used to flow.
All within the broad valley long ago.
With some of the larger lava flows making
it all the way to the Pacific Ocean.
So did the Ice Age Floods make the Columbia
River Gorge?
The answer is no.
Remember, the river was here before the modern
Cascades, and the mountains uplifted against
the river to make the Gorge.
But the Ice Age Floods did leave their mark!
The famous Ice Age Floods impacted much of
the Pacific Northwest over the last 2 million
years.
An ice dam in northern Idaho created Glacial
Lake Missoula.
Repeated failures of the Purcell Ice Lobe
meant 100 Missoula Floods across eastern Washington.
And one truly impressive flood from Utah,
the Bonneville Flood, followed the Snake River
in southern Idaho, cruised through Hells Canyon,
and entered the Columbia River at Pasco, Washington.
A temporary backup, Lake Lewis, formed at
Wallula Gap, the eastern gateway to the Columbia
River Gorge.
Every Ice Age Flood passed through the Columbia
River Gorge on its way to the ocean.
The biggest floods through the Gorge?
An estimated 10 million cubic meters per second,
that’s 300 times greater than largest historical
flood on the Columbia River.
The highest trimline at The Dalles is consistently
at 960 feet elevation.
And a bit downstream at Rowena Point, the
floods really ripped into the bedrock.
There’s scablands here like out in eastern
Washington.
Classic features due to Ice Age Floods erosion.
The scablands at Horsethief Butte are particularly
impressive.
Giant potholes and a basin and butte topography.
And some of the largest floods overtopped
a river-parallel ridge on the Oregon side.
Giant flood bars were deposited.
Tons of rocks dumped in quiet spots south
of the river.
Radiometric dates from material within the
giant deposits means there’s a long history
of Ice Age Flooding here.
Not just floods since 18,000 years ago, which
is the time frame usually presented to the
general public.
So did the Ice Age floods cruise through the
Gorge at maximum speed?
And what’s with all of those tilted layers
of bedrock?
The tilted beds of the Columbia River Gorge
are from plate tectonic forces applied to
originally flat bedrock layers.
But be careful, these tilted beds are not
related to the Cascade Uplift that we talked
about earlier.
Instead, the Yakima Fold and Thrust Belt,
a family of folds and faults in central Washington,
intersect the Gorge.
The crust of the Pacfic Northwest has been
slowly rotating clockwise for millions of
years into a nonrotating northern Washington
and Canada.
The result?
Anticlines and synclines, reverse and thrust
faults.
They all formed from crustal squeezing.
Warps and cracks in the crust that formed
after the Columbia River was established here.
You want proof?
The Columbia River makes an abrupt turn at
Rowena and cuts right through the Columbia
Hills Anticline.
You can't do that unless the river was here
first and the ridges came second.
In the middle of the The Dalles Syncline,
a broad downfold, volcanic mudflows of the
Dalles Formation are preserved.
It’s not all basalt around here.
But here’s a key point.
The Yakima Folds and Faults have made narrow
constrictions for the river to flow through.
Wallula Gap was not the only choke point for
the floods on their way to the Pacific.
Many prominent valley constrictions, chokepoints,
exerted significant control on Ice Age flood
hydraulics.
Wallula Gap, Rowena Gap, Bingen Gap, Crown
Point.
The water accelerated to 60 miles per hour
at these bottlenecks, but just downstream
from each constriction?
Giant Flood Bars composed of loose rocks that
the floods dropped as the water spread and
slowed.
The whole town of Lyle, Washington sits on
a flood bar downstream of Rowena Gap.
The bar used to extend across mouth of the
Klickitat River.
The Mosier Flood Bar sits where Ice Age floodwater
diverted up a side valley.
The Town of Bingen sits on a huge flood bar
downstream of Bingen Gap.
And on an even larger scale, much of East
Portland sits on a huge Ice Age flood bar
downstream of Crown Point.
Now, for all those questions about specific
attractions in the Gorge.
Iconic images of Native Americans harvesting
and processing salmon at Celilo Falls.
Where can I find those falls, you say.
Before they closed the gates on The Dalles
Dam in 1956, Celilio Falls was a majestic
place.
When the river was low, Celilo had a sheer
drop of 18 feet.
In the reach downstream, narrow chutes were
separated by large holes in the river bottom.
Holes 130 feet deep.
Drilled by the Ice Age floods.
That’s 100 feet below sea level.
The sets of rapids, The Dalles of the Columbia,
dropped the river 80 feet in 12 miles.
And immense salmon runs fought their way up
through the falls and chutes.
Celilo Falls is no more.
Buried under still water behind The Dalles
Dam.
Downstream where the river passes through
the center of the Cacades.
There’s a very different reason that the
river is choked down here.
Lewis and Clark in 1805 took note of large
stands of partially submerged tree stumps.
A Submerged Forest of the Columbia.
Trees up to 25 feet tall.
Thousands of drowned stumps upriver as far
as The Dalles.
And Lewis and Clark were about to encounter
a set of rocky rapids here.
The Great Shoot they called it.
The Cascades of the Columbia.
In this same spot, Native Americans spoke
of a Bridge of the Gods.
A legend of river crossing without getting
feet wet.
And not an ancient legend.
Fathers voyaging upriver in their canoes without
obstruction as far as The Dalles of the Columbia.
What happend here?
An enormous landslide.
The Bonneville Landslide.
Part of the Washington side of gorge slid
down and buried Columbia River channel with
300 feet of loose rocks.
The slide pushed the river a mile south towards
Oregon making a landslide dam 3 times higher
than today's Bonneville Dam.
And above the slide?
Impressive cliffs.
The head scarp of the slide where the mountain
split.
Upstream of the slide, the river rose 40 feet.
The Lake of the Gods extended tens of miles
upstream.
Today’s Skamania Lodge would’ve been lakeshore
property.
The lake eventually overtopped the rock blockage
and drained.
After cutting a passage through the slide
down to its current bed, the rapids first
made their appearance.
Lewis and Clark’s Great Shoot rapids?
Boulders from the toe of the Bonneville Landslide.
Rocks too big for the river to flush through
the gorge.
Later in the 1800’s, locks were built to
negotiate the rapids, the landslide blocks.
Today, the rapids, as well as most of the
Cascades Locks and Canal, are underwater.
Drowned in 1938 by the reservoir behind Bonneville
Dam.
So what’s the age of the Bonneville Slide?
It was before Lewis and Clark right?
Before 1805?
Maybe the slide was triggered by the Great
Magnitude 9.0 Earthquake that struck all the
Pacific Northwest on January 26, 1700.
Tree rings were counted in cores from 50 living
trees growing on top of the landslide.
The result?
Nope.
Not from the 1700 quake.
Those trees as old as mid 1500’s.
And radiocarbon dating from the submerged
trees gives us mid 1400’s AD as a confirmed
date.
So the Bonneville Landslide, the Bridge of
the Gods, they blocked the Columbia River
around the year 1450 AD.
More than two centuries before the Great Earthquake
and more than three centuries before Lewis
& Clark.
So what triggered the Bonneville Landslide
and so many other prehistoric landslides on
the Washington side of the gorge?
The bedrock is the answer.
700 feet of Columbia River Basalts overlie
900 feet of Eagle Creek Formation, layers
of volcaniclastics and mudflows.
All of those layers tilt south toward the
river.
A well-greased skidboard where rainwater penetrates
the cracked basalts and concentrates at a
clay layer.
Landslides in the Columbia River Gorge are
part of the past and our future.
The layers still dip, the clay is still there,
and it still dumps rain in the heart of the
Gorge.
Continuing downstream, another familiar landmark.
Beacon Rock.
Hey, is this one of those intracanyon flows?
No.
Beacon Rock is an 850 foot high remnant of
an eroded volcanic neck that's only 57,000
years old.
Think today’s Lava Butte in central Oregon.
A volcano that formed in middle of the river.
Lava would dam the river on occasion, but
the volcano no match for the river.
And back in the early 1900’s, Henry Bittle
built steps to top.
Walk your familiy up the center of a volcano.
The glorious waterfalls in the Gorge.
Multnomah Falls and others.
Why are there so many here?
They are primarily the result of Ice Age cutting
by the Columbia River against an uplifting
Cascade Range.
The gorge cutting prompted landslides from
the Washington side to push the river to the
south side of the Gorge, which repeatedly
undercut thick, stubborn, older Columbia River
Basalts.
The Ice Age Floods swept through the gorge
on occasion to clean up the walls, but the
waterfalls are really a direct result of tectonic
uplift.
After all of this geologic history, and after
Lewis and Clark, European-based settlers began
arriving.
The Oregon Trail approached the Gorge from
the east.
And the Old Moody Road was a primary route
along the southern edge of the Columbia River.
The heart of the Gorge lay ahead.
A giant obstacle.
How to proceed?
The wagon trains decided, well, are we gonna
get wet by following the river or are we gonna
stay dry by climbing up and over the Cascades
near Mt Hood?
The Dalles up ahead became a major stop for
the Oregon Trail travelers to ponder that
question.
Decades after the Oregon Trail, early steamboats
cruised up and down the river.
And then in 1915, the first successful highway
to cross through the Cascade Range.
The Columbia River Highway was constructed
to harmonize with the beauty of the Gorge.
Graceful sets of curves separated by viaducts,
bridges, tunnels all faced with natural stone
worked by European masons.
A brand new Vista House presided over an amazing
landscape suddenly accesible by automobile.
With the grand opening of the highway in 1915,
a young geologist, J Harlen Bretz, was hired
to write a roadside geology guidebook.
His first taste of deposits and landforms
that got him thinking for the first time about
huge floods of water from a then-unknown source.
A controversial topic that initally bring
him scorn and ridicule, but eventually brought
him fame and acceptance worldwide.
Of course, the wild Columbia River was tamed
in the 20th century to harness the power of
the river.
A continuous string of reservoirs ending at
tidewater at the foot of Bonneville Dam.
Today, the Columbia River Gorge National Scenic
Area, with the Discovery Center at its hub,
is famous for its hundreds of hiking trails
and gorgeous wildflowers.
The National Scenic Area designation allows
for preserving the scenic quality by regulating
land use and development, and through property
acquistion.
All of this geology has forced barges, salmon,
railroads, and highways through this narrow
slot through the Cascades.
Geologist Jim O’Connor has devoted many
years to advancing our understanding of the
geology of the Columbia River Gorge, and his
work is not done.
By dating various young lavas that came into
the Gorge at various elevations, like the
pillows in the freeway roadcut just west of
Hood River, we can improve our grasp of the
timing of the Cascades uplift and the river’s
down-cutting.
More work is also needed on the history of
river blockages here.
So many lava dams.
And landslide dams through the history of
the Gorge.
How did those blockages affect ancient fish
populations?
Stay tuned.
Like all branches of the sciences, there are
always new questions that geologists will
work to answer.
An awe-inspiring place.
The Columbia River Gorge.
A beautiful geologic laboratory for all to
enjoy.
