From Washington To You
Basalt walls and canyon floor in Moses Coulee on the Columbia Plateau.
Photograph by the Bureau of Land Management Oregon and Washington. Public domain.

From Washington to you

Moses Coulee Gravel Bar

Great Gravel Bar of Moses Coulee · Douglas County · Ice Age floods

A teardrop of pebble-cobble gravel 3.2 miles long and 240 feet high — perhaps the largest flood bar in the Channeled Scabland.

The Great Gravel Bar of Moses Coulee is a National Natural Landmark on the Ice Age Floods trail. NPS says an outburst from Glacial Lake Missoula was diverted into Moses Coulee when the Okanogan Lobe blocked the Columbia about 14 miles north of the site. In a single flood the coulee became a long, deep canyon second only to Grand Coulee.

As the flood waned, a 200-foot sheet of gravel covered the coulee floor. Behind a bedrock protrusion a giant teardrop-shaped pendant bar formed. The bar is 5.2 kilometers (3.2 miles) long and as much as 74 meters (240 feet) high — perhaps the largest flood-related bar in the scabland. The coulee here is about 180 meters (590 feet) deep and 1.5 kilometers (1 mile) wide.

Most boulders on the bar are basalt plucked from the walls upstream. A few granite and other non-basalt boulders were likely ice-rafted on bergs. An elongate depression about 0.6 mile long on the west side records eddy circulation during deposition. The sources below are the National Park Service landmark page.

  • Geography & Geology

Sources (1)

Last reviewed: September 21, 2026

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