From Washington To You
The dry Grand Coulee and Crescent Bay before reservoir flooding, about 1940.
Photograph from the National Park Service, NPGallery, circa 1940. Public domain.

From Washington to you

Grand Coulee

Grand Coulee · Grant County · Ice Age floods

A dry canyon about 50 miles long holds the geologic story of a river that lost its channel — until people flooded part of it as Banks Lake.

Grand Coulee is a National Natural Landmark on the Ice Age Floods trail. NPS says this geologic feature is approximately 81 kilometers (50 miles) long. From Dry Falls State Park, about 5 miles southwest of Coulee City, visitors can see much of the evidence.

The landmark page walks through a series of events: the ancestral Columbia flowed through a low range of granite mountains; lava built the Columbia Plateau and diverted the river; ice advanced and receded; a new course was cut; waterfalls formed and retreated; and the Columbia returned to its present channel, leaving the Coulee high and dry until part of it was turned into a reservoir by damming.

That reservoir is Banks Lake, behind Dry Falls Dam, fed from Grand Coulee Dam. This card is the canyon. The dam and the lake are separate cards. The source below is the National Park Service landmark page.

  • Geography & Geology

Sources (1)

Last reviewed: September 21, 2026

Keep wandering

  • nearby

    Banks Lake

    Reclamation's equalizing reservoir for the Columbia Basin Project sits behind the Feeder Canal from Grand Coulee, the first stop for irrigation water heading south.

  • nearby

    Dry Falls

    A 3.5-mile cliff in the Grand Coulee is the lip of a waterfall that once dwarfed Niagara.

  • nearby

    Grand Coulee Dam

    A Depression-era dam turned the Columbia into irrigation, power, and a 151-mile lake.

  • same landscape

    Ice Age Floods

    NPS says that 18,000 to 15,000 years ago an ice dam in northern Idaho failed, sending Glacial Lake Missoula across Washington and down the Columbia.