Must-See Pacific Northwest Ice-Age Marvels

12 Ice-Age Wonders You Still Can Witness Today

You don’t have to travel far in the Pacific Northwest to see the impacts of the floods that reshaped the region some 15,000 to 18,000 years ago. This was during the last glacial cycle, when a massive ice dam across the Clark Fork River near present-day Sandpoint, Idaho, broke apart, releasing the contents of a 2,000-foot-deep lake in a matter of days.

The outflow from what is known as Glacial Lake Missoula, believed to have stretched for some 200 miles east and containing more water than lakes Erie and Ontario combined, raged across the Idaho Panhandle into the Spokane Valley, before splitting into three directions: south to the Snake River; west into the Grand Coulee, a long-since-dried riverbed on the Columbia Plateau; and southwest to Crab Creek. After reaching the Columbia River, the waters made a canyon-carving, valley-filling rush to the ocean.

Over the next 3,000 years, the ice dam is believed to have re-formed and collapsed as many as 90 more times. Although they occurred before people are known to have inhabited the Northwest, the influence of these ice-age floods, aka the Missoula Floods, over our region’s natural and human history is beyond profound. Yet these cataclysms were virtually unknown until geologist J Harlen Bretz proved their existence to a skeptical scientific community in the mid-20th century.

In 2009, Congress authorized the creation of the 1,100-mile-long Ice Age Floods National Geologic Trail to link features created by the floods with signs, maps and improved public access.

Because of COVID-19, please take recommended health precautions if you decide to explore outdoors.

Frenchman Coulee

Frenchman Coulee. Photo by DFeinman/Getty Images

1. Frenchman Coulee

Carved out of basalt, Frenchman Coulee and the Feathers near George, Washington, offer spectacular examples of the floodwaters’ power. Rushing walls of water ate away at columns on the coulee walls and brought down tons of rocks and huge boulders. Getting there: A short trail to view the coulee walls is off Vantage Road, about 9 miles southwest of George.

2. Astoria, Oregon

Some evidence of the ice-age floods is deep under water, where the deluges emptied into the Pacific Ocean. Torrents deposited gravel and silt onto the seafloor for dozens of miles west of today’s shoreline, and as far away as 400 miles southwest, off Northern California’s coast.

3. Lincoln Avenue, Vancouver

Researchers believe the waters flooded the present-day Portland-Vancouver area at depths of up to 400 feet. Undulations in places such as N.W. Lincoln Avenue in west Vancouver are believed to be giant ripple marks left by the floods. Getting there: Ripples can be seen along N.W. Lincoln Avenue between N.W. 51st Street and N.W. 59th Street.

Beacon Rock

Beacon Rock. Photo by RDParis22/Getty Images.

4. Beacon Rock

Beacon Rock, the 848-foot-tall sentinel of the western Columbia River Gorge, is the solidified, once-molten neck of an extinct volcano. The river and the floods swept away the cinder cone in which it was encased. A trail to the summit is 1.8 miles round-trip. Getting there: The landmark and its namesake state park are 35 miles east of Vancouver and 10 miles west of Stevenson, off State Route 14.

5. Yakima Valley Rhythmites

These rhythmically bedded soil layers near Zillah are believed to have been deposited by waters backed up behind Wallula Gap, during separate floods. Similar rhythmites are visible in the Walla Walla area and elsewhere. Getting there: Visible along the north side of Interstate 82, between mileposts 52 and 54.

6. Bellevue Erratic — Erratic Rock State Natural Site

About 30 miles down the Columbia River from Vancouver, waters slammed into the Kalama Gap choke point and backed up on the Willamette Valley as far south as Eugene. Ice chunks, carrying rocks from as far away as British Columbia, dropped out along the way. The largest of those rocks in the Willamette Valley is the 90-ton Bellevue Erratic, at Erratic Rock State Natural Site. Getting there: The site is about 6 miles south of McMinnville, off Oregon State Route 18.

Clark Fork River

Clark Fork River. Photo by Different Brian/Getty Images

7. Clark Fork River

Ice dams that collapsed and re-formed up to 90 times on the Clark Fork River, near Lake Pend Oreille, triggered one of the greatest series of floods the world has known. The lake above the dam is believed to have submerged present-day Missoula, Montana, under 800 to 1,000 feet of water.

8. Rowena Slump Blocks

After escaping through Wallula Gap, floodwaters surged down the Columbia River. The basalt Rowena Slump Blocks were chiseled off the cliff below Oregon’s Rowena Crest Viewpoint. Getting there: The loop road to the viewpoint is off U.S. Hwy. 30, about 13 miles east of Hood River.

9. Dry Falls

During the height of the floods, Dry Falls, separating the Upper and Lower Grand Coulee rivers, flowed at 1,000 times the rate of Niagara Falls. The eventual return of the Columbia River to its normal course left Grand Coulee and its 400-foot waterfall dry. Groundwater-fed lakes now fill the former falls’ plunge pools. Getting there: The Sun Lakes–Dry Falls State Park visitors center is 25 miles north of Soap Lake, or 4 miles southwest of Coulee City.

Palouse Falls

Palouse Falls. Photo by Eric Liu08/Getty Images

10. Palouse Falls

The spectacular 198-foot Palouse Falls and its dramatic gorge is the only active waterfall in Washington created by the floods, which carved a route out of pre-existing basalt. Getting there: Palouse Falls State Park is accessible via State Route 261, about 15 miles southeast of Washtucna, or 8 miles north of Lyons Ferry State Park.

11. Drumheller Channels National Natural Landmark

The Columbia Plateau’s channeled scablands, marked by steep, isolated basalt hills surrounded by dried stream channels, offer dramatic evidence of the scale of erosion caused by the floods. The Drumheller Channels are among the finest examples; Bretz described them as “a complex unparalleled elsewhere.” Getting there: The Drumheller Channels are part of the Columbia National Wildlife Refuge, accessible via W. McManamon Road in Othello.

12. Wallula Gap

Southeast of Kennewick, the Columbia River cuts through the 1-mile-wide Wallula Gap, which was too narrow for the floods. Backed-up waters formed temporary Lake Lewis, stretching from Yakima to Walla Walla. Getting there: Visible from U.S. 12 and U.S. 730, aka Wallula Junction. You can have good views from the Twin Sisters Trail, 1.9 miles south of the junction, off U.S. 730 (look for the small parking lot on the east side of the highway).

–Written by Gregg Herrington
–Top image of Wallula Gap by StirlingPG/Getty Images.

This story originally appeared in the July/August 2017 edition of the AAA Washington member magazine, Journey, and was updated in February 2021.

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