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