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Adams County History

Geological History

The Flood That Built Adams County

Adams County looks the way it does because of a flood.

Between 18,000 and 13,000 years ago, a lobe of the Cordilleran ice sheet pushed south and dammed the Clark Fork River near what is now the Idaho-Montana border. Water backed up behind that ice into a lake geologists call Glacial Lake Missoula, standing 2,000 feet deep at the dam. Ice floats. Eventually the dam lifted, failed, and the lake left all at once. Then the ice advanced again, the lake refilled, and the whole sequence repeated, perhaps as many as a hundred times.

Each failure sent water across eastern Washington at roughly 65 miles per hour. Researchers have reconstructed peak discharge near the outlet at about 20 million cubic meters per second, seventeen times the combined flow of every river on Earth today. That water did not follow the existing rivers. It stripped soil down to basalt bedrock, cut new channels where none had existed, and left the landscape we now call the Channeled Scablands. Adams County sits in the middle of it.

When geologist J Harlen Bretz argued in the 1920s that this ground had been carved by catastrophic flooding rather than slow erosion, his profession treated him as a crank. He was right. It took two decades and J. T. Pardee’s fieldwork to prove it.

What the Water Left Behind

Five miles northwest of Othello, the Drumheller Channels are what Bretz called “the most spectacular tract of butte-and-basin scabland on the plateau.” He mapped 150 separate channels and more than 180 rock basins across that ground. The National Park Service designated it a National Natural Landmark in 1986, and it is a featured stop on the Ice Age Floods National Geologic Trail.

The southeast corner of the county tells a different version of the same story. Washtucna Coulee could not carry the volume the floods threw at it, so the water spilled south across the divide toward the Snake River and cut Devils Canyon on the way. The Palouse River still runs today in the channel the flood forced it into.

Between those two extremes, the floods scoured the low ground and left the high ground alone. Those spared ridges carry loess, the wind-blown silt that settled here over thousands of years, deep and fine and productive. The USDA named an entire soil series after our county seat. Ritzville silt loam runs more than a meter deep, and it is the foundation of the dryland wheat ground stretching from Ritzville through Lind and Washtucna.

Why a 15,000-Year-Old Flood Still Matters

Adams County’s economy today rests directly on what that water took and what it left.

In west Adams County, the flood-carved potholes south of Moses Lake were flooded a second time in 1949 behind O’Sullivan Dam to create Potholes Reservoir, the working heart of the Columbia Basin Project. Irrigation water moving through channels the floods cut is what turned the ground around Othello into some of the most productive farmland in the United States. Othello’s potato, onion, and food processing industry exists because glacial meltwater came through here first and left behind a place where water could be stored and moved.

In east Adams County, the loess the floods spared grows wheat with no irrigation at all. The broad, flat, well-drained plateau the floods scoured is the ground that 46 miles of Interstate 90, US-395, and the BNSF Northern Transcon rail line all cross. Ritzville works as a transportation and logistics location today for the same reason it worked as a wheat shipping point a century ago. This terrain is easy to build across and easy to move through.
Lind and Washtucna sit closest to the scabland edge, where the coulees run deepest and the farm ground is hardest won. That geography shaped how those communities grew, what they grow, and how far apart they sit.
None of this is trivia. When we tell a food processor that Adams County has water infrastructure and productive soil, or tell a logistics operator that Ritzville has flat, buildable, well-drained industrial ground on an interstate corridor, we are describing the direct inheritance of one of the largest floods in the planet’s history.

The water has been gone for 13,000 years. Adams County is still living on the returns, and we are just getting started on what comes next.

Sources and Further Reading

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