The storm stretched from the Mexican border up to Oregon and Washington and was expected to last through Tuesday afternoon, said Stan Wasowski, a forecaster for the National Weather Service in San Diego. He said rain clouds extended several hundred miles off the Pacific coast.
"This one here is hitting the entire state," Wasowski said.
Heavy snow forced the closure of a 50-mile stretch of Interstate 5 in both directions in the mountains north of Los Angeles. The roadway is the region's main north-south artery.
"We don't see it opening any time soon," said David Porter, a California Highway Patrol officer.
CBS News correspondent Bill Whitaker reported that the wild weather has created perfect conditions for avalanches - when heavy snow falls atop a base made slick from rain and freezing. Sixteen people have died in avalanches so far this winter, which is the most in more than 30 years.
In Northern California, a flood advisory was issued for the San Francisco Bay area and a flash flood watch was in effect for much of California's central coast, where flooded greens forced the cancellation of the AT&T Pebble Beach National Pro-Am's final round.
The PGA Tour declared Dustin Johnson the winner after he built a four-shot lead on Saturday, before the rain began.
In Southern California, rain brought renewed fears of mudslides in areas ravaged by wildfires last year. The eastern Los Angeles County city of Sierra Madre has warned residents they may need to leave their homes, and a voluntary evacuation order was in effect early Monday.
Up to 7 feet of snow had fallen in the Sierra Nevada over the past week, and more was expected by early Tuesday. Tire chains were needed to navigate steep mountain passes, but the weather was a boon for Lake Tahoe resorts, where skiers and snowboarders were enjoying heaps of fresh powder.