The crash was reported about 3:15 p.m. along U.S. 2, just east of Skykomish, said trooper Mark Francis with the Washington State Patrol.
Investigators believe a Toyota 4Runner was westbound on the highway when it crossed the center line and struck an eastbound plow.
The impact caused the Toyota to flip and also strike a Volvo station wagon.
The Volvo's driver was taken to a local hospital with serious injuries, Francis said. No other injuries were reported.
Troopers were still on scene Wednesday evening without cellphone service, so details were preliminary. Traffic was down to one lane in the area for some time.
The Toyota driver was arrested for investigation of vehicular assault and driving under the influence.
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