A winter storm is sweeping California, battering the south with heavy rain and high winds, and dumping snow on the Sierra Nevada mountains.
At least 440,000 people were left without power from central Oregon to Washington State, roads were closed and flights cancelled at some airports.
Areas denuded by October's forest fires are braced for flooding and mudslides.
Emergency services have asked at least 3,000 people living in Orange County canyons to leave home as a precaution.
Flash flood warnings were issued for most of Los Angeles County and home-owners have been protecting their property with sandbags and hay bales, the Associated Press reports.
"There's a little bit of a let-up right now in the rain but there's still a huge band of rain that's going to come in today," Ted MacKechnie, a US National Weather Service forecaster, said on Saturday morning.
There were no immediate reports of deaths or serious injuries.
In the Sierra Nevada, the range of mountains which runs up the centre of California, snow forced the closure of Interstate 80, the main east-west link between northern California and Nevada.
Up to 44 in (112cm) fell overnight in some parts of the range, and depths of up to 10 ft (3m) are forecast at higher points by Sunday.
Up to 2 ft (0.6m) may fall on the popular tourist spot of Lake Tahoe.
Flights in the San Francisco area were grounded and storm winds meant large lorries were banned from the Golden Gate Bridge.
The tourist attraction of Alcatraz Island out in the bay was closed to tourists.
Forecasters believe the blizzard conditions and heavy snow will begin to subside by Sunday as the cold front moves east.