The Sonoma County Sheriff Office said all roads leading into the community of Guerneville were flooded. The nearby town of Monte Rio also was isolated when roads leading to it were swamped.
The river frequently floods in rainy weather, but it had not reached this level in more than two decades.
But it reached almost 46 feet Wednesday night, and the National Weather Service predicted that major flood conditions will continue Thursday because it will take time for all that water to recede.
The river reached its crest Wednesday night at 45.4 feet.
The affected areas have been caught in what meteorologists call an 'atmospheric river, ' which is a long, narrow stretch of water vapour that can cause heavy rainfall and flooding when combined with strong winds.
Water inundated areas around Guerneville, a community of about 4,500 people.
Travel could be hard to impossible in some mountain passes above about 6,000 feet, says the National Weather Service.
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The estimated 2,000 buildings inundated by floodwaters were mainly in and around the community of Guerneville, said Briana Khan, a Sonoma County spokeswoman.
Other waterways, including the Napa River, also were expected to overflow their banks as an ocean-spanning plume of moisture continued tracking through the West. Snow from the storms closed roads and schools and toppled trucks and trees from OR to Montana.
Forestville, a small Sonoma County town about 13 miles west of Santa Rosa, sits along the Russian River. However, more than 200 miles (320 kilometers) north, a man drowned while trying to reach his Humboldt County home by walking through about 5 feet (1.5 meters) of water.
"I could not afford to buy flood insurance", she said.
Crum said Wednesday that those who made a decision to stay stocked up on food and drinking water.
"We're all pretty shaken up about what happened and thinking what could we have done differently", Alexandre said.
Those rescues included two women found drifting in a boat with no paddles and a newspaper delivery driver whose truck ran off the road into 10 feet (3 m) of water, county Sheriff Mark Essick told reporters. Miami and Houston put up with hurricanes.
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However, Bridges said it will take weeks to clean up his R3 Hotel, as he has done in past floods.
Their homes surrounded by flood waters, they have been moving around on kayaks and canoes.
"Anything that's been flooded you've got to rip it out, sanitize everything.and rebuild", he said, but added nonchalantly: "Everything's fixable".
The storm is expected to continue until Friday, bringing with it rain, wind and snow, making travel into the Sierra Nevada mountain range risky.
The National Weather Service categorizes any floods above 45 feet as "disastrous" for Guerneville, predicting that almost all its downtown will flood at that height.
Deputies have also helped people get out of cars stuck in floodwaters.
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