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100.010 Geology & Climate

Prominent geologist John Eliot Allen wrote that, “The geologic evolution of the Columbia River
Gorge is a result of 40 million years of predominantly volcanic activity.” But, he added that “it
also involves faulting, folding, uplift and subsidence, erosion and sedimentation, repeated
northward movement of the [Columbia River] valley, a period of cataclysmic flooding, and
finally extensive landsliding. The Gorge thus exhibits a remarkable diversity of geologic events,
dating back millions of years, and matched by few other places in North America.” Periodic ice
age flooding on the Columbia, between 12,800 and 15,000 years ago, stripped the eastern part of
the Gorge of its topsoil and scoured out channeled basalt areas known as scablands near The
Dalles. They also left in their wake hanging valleys in the Gorge’s narrowest part, turning
mountain streams into the many cascading waterfalls seen there today. The walls are also
crumbling into the river, forming huge talus slopes and landslides of as much as 14 square miles.
Volcanism created the Cascade Mountains. Geologically speaking, the entire Gorge is young
and unstable, and is the only location along the range of mountains consisting of the Cascades
and the Sierra Nevada where a river cuts though from east to west, to the sea.

Hadlow, Landmark Nomination, 13

Following the uplift of the Cascade Range in the eons for the geologic past, the impounded waters of a vast inland sea lay over the eastern part of Oregon and beyond.  When the disturbance of this uplift had subsided, the waters began the task of opening a way through this barrier to the new shores of the ocean.  This almost direct channel is now generally known as the Columbia Gorge.  Except by the Columbia River, the Cascade Mountains are unsevered from the Klamath River gap, near the Oregon-California line, to the Frasier River in British Columbia.

In this deeply worn and notably scenic Gorge there is visible evidence of the titanic forces that opened this great chasm and enriched the picturesqueness of Oregon and Washington with its towering slopes of rock and forest.  These are marked by stupendous cliffs with immense taluses below them; there are monoliths, great and small; interesting side canyons breach the walls, with beautiful high waterfalls plunging into sylvan dells, all in a constantly unfolding panorama of extraordinary scenic features.  However, as pleasing and inspiring as all these may be, the everlasting and crowning glory of the Gorge is the silent majesty of the mighty Columbia itself.  In the eras of the past it was this then greater river that had worn down through thousands of feet of Columbia basalt, layers of andesite, cemented beds of Satsop gravels, Carson lavas and into the Eagle Creek formation, the lowest stratum exposed so far.  -W. A. Langille, State Parks Historian, 1946 (Langille and Boardman 3 - 4)

Because of various physical factors, the Oregon and Washington sides of the Gorge differ markedly in their geomorphology and ground cover.  The Oregon portion consists of high cliffs and deep canyons running perpendicular to the Columbia River.  The altitude of the Oregon side varies from about 600 to 700 feet at the west end to a high point of almost 5,000 feet near the eastern boundary, with an average elevation range of between 3,500 and 4,000 feet.  The western half is covered with extremely lush vegetation and many waterfalls plunge over the cliffs in spectacular cataracts.  However, as you travel east the aridity increases, forests become less dense and waterfalls scarce.

The mountains on the Washington side of the Columbia River are neither as rugged nor as well-timbered as those in Oregon, although several major peaks on the edge of the Gorge rise as high as 2,500 to 3,500 feet.  Several landslides have occurred, one of which blocked the Columbia River near the legendary Bridge of the Gods, a span which the Indians believe joined what is now Oregon and Washington.  Years ago a fire called the Yacolt Burn swept through the southwestern Washington Cascade Mountains and its destruction is obvious from the many denuded hills and burned snags.  (Lowe and Lowe, 100 Oregon Hiking Trails.  33)

Columbia River

The Columbia River drops 2,650 feet from its source at Columbia Lake in the Canadian Rockies to its mouth at sea level near Astoria, Oregon.  Tapping that latent power was key to transforming the vast Northwest wilderness.  Stewart Holbrook, the great chronicler of the Columbia River, wrote of the rivers carving power:

Gravity, pressure and time took it through the Cascades in the first place, and to get through, the stream had to undermine mountains, crumble them and dig a channel which men have plumbed and found to reach a depth of 300 feet below the surface water, and 215 feet below sea level.  In a river this is an extraordinary depth.  So is the force that made it.  (Holbrook , qtd. in Durbin 14) 

Of the river's 1,200 miles from source to mouth, only 57 river miles remain free-flowing today.  (Durbin 18)

Waterfalls

There are 25 mapped waterfalls in the Columbia River Gorge, and eleven can be seen from
Interstate 84 or the CRH. The south side of the Gorge has the largest concentration of high
waterfalls in North America.

Hadlow, Landmark Nomination, 13

Climate

The Columbia River Gorge is an area of wide-ranging climatic and vegetative growth patterns.
The Cascade Range is a barrier to the eastward movement of moist air from the Pacific Ocean.
Rainfall averages 42 inches annually west of the mountains. Levels of 100 to 150 inches at the
middle of the Gorge are not uncommon. However, precipitation at The Dalles is about 14 inches
annually. This rain shadow effect causes the striking and rapid transition in vegetation from the
Cascades’ moist west slopes to central Washington and Oregon’s dry plateau.
Because the Gorge is a near sea-level channel through a mountain range with peaks such as
Mount Hood rising to heights greater than 11,000 feet, it also has a vertical gradient of differing
environmental conditions. The steep side canyons, for instance, clasp in their walls damp
microclimates unique to the region for their plant and animal life. The exceptional combination
of natural, geological, cultural, and scenic resources led to the Gorge’s designation as a national
scenic area in 1986.  (Hadlow, Landmark Nomination 14)

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Geologic History of the Columbia River Gorge
From: U.S. Army Corps of Engineers, Portland District, and the U.S. Department of the Interior, U.S. Geological Survey, The Geologic History of the Columbia River Gorge: Information Brochure.
http://www.columbiariverhighway.com/columbia-river-gorge-geology.htm
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