Explore the geology and sites to see in the Columbia River Gorge, which features plenty of columnar basalt, hydroelectric dams, and several large waterfalls.
Happy Thursday! After visiting Mt. St. Helens last week, we’ll stay in the Cascades and head toward Portland this week, traversing the Columbia Plateau, and taking in the magnificent Columbia River Gorge. Who’s ready to see some columnar basalt?
Sharon Lyon
Editor, GeoLifestyle
The Columbia Plateau
Columnar basalt; Columbia Plateau in Washington State
The Columbia Plateau stretches across parts of Washington, Oregon, and Idaho. It formed as a massive flood basalt.
During the early Miocene and early Pliocene (17–6 million years ago), the North American plate migrated over a stationary hotspot. Numerous linear vents erupted lava near the eastern edge of the plateau, engulfing more than 63,000 square miles, and accumulating a thickness of more than 6,000 feet. The hotspot is currently situated beneath Yellowstone National Park.
As the molten rock came to the surface, the Earth’s crust gradually sank into the space left by the rising lava.
Over 300 high-volume lava flows have been identified and divided into seven formations, collectively known as the Columbia River Basalt Group. As the basaltic lava cooled, it contracted and cracked, forming columnar jointing, usually hexagonal in shape.
At the same time, the region was experiencing intense compression, transforming the original, horizontal layers of flows into ridge-forming, narrow anticlines and valley-forming, broad synclines.
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The Columbia River Gorge is a spectacular river canyon that's 80 miles long and downcuts to a depth of 4,000 feet. The gorge divides Washington and Oregon and is the only major break in the Cascade Range in the United States.
The ancient Columbia River was forced into its present course by the northwesterly advancing flood of lava. In the late Miocene, the Columbia River drained the relatively low plateau.
When the Cascades began to rise 7 million years ago, the basaltic rock was exposed to the incision and entrenchment of the Columbia River. As the range grew, erosion from the river was able to keep pace, carving out the gorge.
In the Pleistocene, the Missoula floods repeatedly inundated the gorge, undercutting the valley walls and triggering landslides. Outcrops of scoured basalt more than 300 feet above sea level provide evidence of the height and destructive power of the flood waters that widened and deepened the Columbia River Gorge.
Learn more about the geology of the Columbia River Gorgehere.
Visiting the Dams
The Columbia River has been harnessed by a series of massive dams; there are 60 in the watershed, with 14 on the Columbia and 20 on the Snake. These hydroelectric dams generate one-third of the electricity used in the Pacific Northwest.
In addition to producing hydroelectric power, the dams aid navigation, control floods, and provide water for irrigation. The reservoirs offer opportunities for fishing, boating, windsurfing, and/or kiteboarding.
The first federal lock and dam on the Columbia and Snake Rivers was the Bonneville Dam, completed in 1943 as part of President Franklin D. Roosevelt’s New Deal. Its purpose was to improve navigation and provide hydropower. Here’s how to visit:
Visitor Centers:
There are two visitor centers at the Bonneville Dam, the Washington Shore Visitor Center on the Washington side, and the Bradford Island Visitor Center on the Oregon side. (The Bradford Island Visitor Center is closed for repairs and will reopen on January 2, 2025).
The centers highlight the fundamentals of electricity and the importance of hydroelectric dams to the region. Learn about the natural and cultural history of the area and the importance of salmon. At the Washington Shore Center, you can view the generators from 85 feet above the powerhouse floor. They are enormous!
At both centers, you can view the fish passage facilities that enable fish to migrate past the dam. Visiting during the fall will coincide with the adult Chinook and coho salmons’ migration up the Columbia to spawn.
On the Oregon side, the hatchery is used for adult collection, egg incubation and rearing of Tule fall Chinook, rearing, adult collection, and spawning of Coho salmon, and rearing of summer and winter steelhead.
One fun thing: Inside the fish hatchery, visitors can see the 10-ft-long, 500-pound Herman the Sturgeon through an underwater window. He’s 89 years old and a celebrity around these parts!
Oregon’s Waterfalls
Stephen Moehle/ Shutterstock.com
Drive the Historic Columbia River Highway back to Portland, and view the magnificent waterfalls, including Multnomah Falls, Wahkeena Falls, Bridal Veil Falls, and Shepperd’s Dell.
Because the basalt layers on the Oregon side of the Columbia River dip away from the river, more sheer cliffs, and consequently more waterfalls, have formed on the Oregon side of the Columbia River Gorge than on the Washington side.
Stop atMultnomah Falls, the tallest waterfall in Oregon, reaching 620 feet.
The falls drops in two tiers along the face of the basalt. Take the trail to the footbridge and the upper observation deck. It is a steep switchback, but you won’t be disappointed.
Six volcanic flows are visible in the cliff face, representing more than 400,000 years of geological history. From late May to early September, reservations are required.
As you fly out of Portland, look out your window at scenic Mt. Hood, the Oregon volcano most likely to erupt. You don’t have to worry—the USGS considers it only ‘potentially active.’
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