Updated

After days of relentless rain, Southern California is starting to feel the most intense storm system yet, with evacuations ordered, roads covered by water and mud, and residents anxiously eyeing already saturated mountainsides denuded by wildfires.

Forecasters expected more rain across the state Wednesday, but the focus clearly was on Southern California where a monster storm was expected to bring torrential rain, thunderstorms, flooding, hail and possible tornadoes and water spouts.

Forecasters warned of possible rainfall rates of up to 1 inch an hour and thunderstorm rates of 2 inches an hour in the region.

Steady rain began falling late Tuesday and was expected to intensify into early Wednesday.

"It's going to be a three-ring circus," said National Weather Service spokesman Bill Hoffer. "There's going to be a six-hour time frame in the early morning when it's really going to be dumping on us."

A rain-soaked hillside collapsed on part of a busy Interstate 10 transition road as overwhelmed drains left hubcap-deep pools of water on roadways littered with fender-bender crashes.

The landslide covered three lanes of the transition in the Pomona area, and the California Highway Patrol shut down part of the ramp before Wednesday morning's rush hour.

In Orange County, rain-loosened boulders and mud blocked access to mountain homes in Silverado Canyon near the Cleveland National Forest, where firefighters were helping evacuate 25 to 30 people whose homes were threatened by rolling boulders and debris flows.

Officials on Tuesday ordered evacuation of 232 homes in La Canada Flintridge and La Crescenta, foothill suburbs of Los Angeles below steep hillsides that burned in 2009 and where mudslides inundated homes and backyards in February.

Walt Kalepsch said his backyard filled with mud and debris last winter, but he planned to stay the night with his wife and daughter.

"If it gets really terrible, we'll leave. But we've been evacuated so many times, it's like the city's crying wolf," he said. "During the rest of the year, it's absolutely gorgeous. It was just one big wildfire that changed everything."

As the "Pineapple Express" system swept Pacific Ocean moisture across Nevada, Arizona and Utah, Gov. Arnold Schwarzenegger declared a state of emergency in six counties.

The huge and powerful low pressure system off the West Coast pushed precipitation right into the Great Basin.

"It takes a lot of energy to push that moisture over the mountains," said NWS meteorologist Dave Bruno. "This kind of storm could march right across the country and create a lot of bad weather along the way. It could affect the Southern Plains on Thursday and Friday. If it sticks together it'll hit Florida by Saturday."

With rain falling up and down the state, Sierra Nevada ski resorts boasted of record-breaking December snowfall, with the storms bringing a total of 10.5 feet to 15.5 feet to Mammoth Mountain.

Rescuers had to pluck some stranded motorists from rain-swollen creeks. Shoppers dodged puddles while buying last-minute Christmas gifts. Disney resorts canceled a plan to shower visitors with artificial snow.

Water content in the snow pack in California's mountains was at 197 percent of normal and 169 percent of the average measurement for April 1 -- traditionally the date when the snow's water content is at its peak, said Ted Thomas, spokesman for the California Department of Water Resources.

As the snow melts, that water will run off into reservoirs that feed the state's extensive agriculture and city water systems.