New map reveals more about prehistoric floods that shaped Washington

 

One of the most formative periods of Washington history came near the end of the last ice age, when warming temperatures led to periodic breaks in the gargantuan dam formed by the Cordilleran Ice Sheet to create Glacial Lake Missoula on the Clark Fork River in western Montana.

Dam breaches unleashed some 40 cataclysmic floods during two millennia 15,000 to 13,000 years ago that carved through bedrock as they swept over Washington into the Columbia River and out the Pacific Ocean.

Drum-Heller-Channels

Left behind are exposed plateaus, steep canyons and some of the most fertile soil in the world.

Thanks to DNR’s Division of Geology and Earth Resources, you can take a brand new look at how flood after glacial flood created the Cheney-Palouse tract of Channeled Scablands in Southeastern Washington.

Using elevation data, the map reveals where flood waters carved through the earth to create the Palouse River, Union Flat Creek, Cow Creek and Rock Lake. Flood features are so huge, they can be seen from space.

Combines harvest wheat grown in rich loess soil near Dusty.
Combines harvest wheat grown in rich loess soil near Dusty.

Higher elevation areas adjacent to flooded channels were covered in windblown silt known as loess, which created the Palouse Hills, which has some of the most agriculturally-productive soil in the world.

You can download this map poster here.

You can also see the modern-day product of these tumultuous Pleistocene floods in person. Take along our roadside guide to the geology of flood basalts and glacier floods so you can know more about what surrounds towns like Pine City, Lamont, Benge and Dusty.

The Karakul Hills east of Sprague Lake provide views of bedrock exposed by these floods.

Rock Lake is the deepest scabland lake (and has legends of a monster swimming within it).

A view downstream from Palouse Falls, taken by O.P. Jenkins in 1923.
A view downstream from Palouse Falls, taken by O.P. Jenkins in 1923.

Or view a rushing torrent of water over exposed Columbia River Basalt at Palouse Falls, formed when Missoula Flood waters overtopped the south valley wall of the ancestral Palouse River and redirected its mouth from the Columbia River into the Snake River.

Find out more about how the Missoula Floods left their mark on Washington from our Geology Library.

You can see more of DNR’s visual presentations about Washington’s geology here.