Communities also saw a rare dusting of snow on the first weekend of 2011 as frigid winter weather marched through Southern California, delaying traffic and stranding motorists, the Los Angeles Times reported.
The California Highway Patrol said the Interstate wouldn't be reopened until it was cleared, possibly Monday or later.
"The entire freeway came to a screeching halt," said Matt Morrow, who was returning to Southern California from a ski trip. "It was snowing like crazy right down there on the freeway."
Morrow told the Times it took nearly an hour for the traffic to move about 100 yards.
In Valencia, Paul Butler said his visiting relatives had to endure bone-chilling temperatures, rainstorms, gusty winds and now snow.
"We were sitting down for the traditional Sunday lunch and all of the sudden, we looked out the window and it's snowing," Butler said. "It's really bizarre. The sky is all white."
The storm system was forecast to drop between 2-8 inches of snow in the mountains, The San Diego Union-Tribune reported.
"Snow levels will be as low as 3,000-3,500 feet, though significant accumulation is only expected above 4,000 feet," the National Weather Service said.
Orange County communities reported rain accumulations of at least a quarter-inch, The Orange County Register reported.
Beginning Tuesday, temperatures were forecast to rise into the 50s to near 60 degrees, the weather service said. Nighttime lows were expected to be in the 30s and 40s.