Heavy rains and flooding also destroyed campgrounds and damaged roads at Mount Rainier National Park, forcing it to close for the first time since Mount St. Helens erupted in 1980.
Meanwhile, a wave of looting hit homeowners in Pierce County, Wash., where police report five burglaries of flooded homes.
"Obviously in a distressed situation, people are going in and kicking doors and burglarizing houses, taking TV's, computers, coins, and anything else that's not tied down," Pierce County Sheriff's Detective Ed Troyer said. "They're heartless people."
The White River flowed over Oregon 35 on Mount Hood's eastern flank on Monday and Tuesday, cutting 20-foot-deep ruts through the pavement and sending boulders and trees rolling down the mountainside, Bill Barnhart, an Oregon Department of Transportation manager, said Thursday.
Two creeks also wiped out a section of the same highway to the north, Barnhart said. Reopening the highway near Mount Hood is estimated to take $20 million.
The storms damaged hundreds of homes and broke rainfall records.
"We have been through it. We'll come through it again. It's just Mother Nature has her own mind," Paul Edwards of Tillamook, Oregon, said.
At least three deaths were blamed on the flooding: two men swept into a Washington river and a 78-year-old woman found along the Oregon coast, where another woman was missing.
Rescue teams also continued to search for hunters who might be trapped in the southwest Washington hillsides between Mount Rainier and Mount St. Helens, officials said Thursday.
Nearly 18 inches of rain fell over 36 hours at Mount Rainier park, one of the crown jewels of the Pacific Northwest. The deluge on Sunday and Monday swamped roads and bridges and cut power and sewer lines.
Initial cleanup will take weeks. Park officials, who assessed some of the damage Thursday, said they hope to return to normal operations by Christmas. In some places, they won't know the extent of the damage until after the snow melts in the spring.
"Some places get that much rain in a year, and we had it in 36 hours," said park spokeswoman Lee Taylor. "When we were finally able to get out and start assessing the damage, it was a very sobering day."
More rain was expected Friday and over the weekend, but it was not expected to be as heavy, said forecaster Chris Burke of the National Weather Service. While river levels were dropping, some were still at flood stage, with recovery and damage assessment still days away.