By GILLIAN FLACCUS
LOS ANGELES (AP) -- After days of relentless rain, Southern California was bracing for 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 heavy rain to move into Arizona, Utah and Nevada on 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. Officials warned of possible rainfall rates of 0.75 inch 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.
"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 Wednesday as overwhelmed drains left hubcap-deep pools of water on roadways littered with fender-bender crashes. The landslide covered three lanes of the transition to State Route 57 in the Pomona area, and the California Highway Patrol shut down part of the ramp before the morning rush hour.
In Orange County, rain-loosened boulders and mud blocked access to mountain homes in Silverado Canyon near the Cleveland National Forest, and firefighters were helping residents walk out of the area. Downtown Laguna Beach was closed as up to a half foot of storm runoff flooded the streets, and mudslides were reported in the San Clemente hills.
Officials on Tuesday ordered evacuation of 232 homes in La Canada Flintridge and La Crescenta, 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 the southwestern U.S., 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."
Flood warnings and emergency declarations were in place in parts of Utah, Nevada and Arizona.
Rushing water ripped through a northwestern Arizona retirement community Tuesday, sweeping away four unoccupied homes near a normally dry river bed and threatening to destroy others.
About 60 miles away, evacuation orders for the entire town of Rockville, Utah -- population 247 -- were lifted after a dam feared close to breaking was declared safe. Nearby Zion National Park also was evacuated and shut down.
In southern Nevada, a state of emergency was ordered after rain-swollen creeks closed some roads in the Las Vegas area and snow disrupted electricity to about 300 customers on nearby Mount Charleston.
With rain falling up and down California, Sierra Nevada ski resorts boasted of record-breaking December snowfall, with the storms bringing 10? to 15? 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.
At least six people were rescued from their cars in Laguna Woods before dawn Wednesday after they drove around barricades on flooded roads, authorities said.
Downtown Los Angeles received more than a third of its annual average rainfall in less than a week.
Parts of the San Gabriel Mountains got more than 18 inches of rain since Friday, with coastal cities like Santa Monica and Long Beach getting more than 6 inches, the National Weather Service said.
Mudslides are a significant risk for three years after a fire and are especially likely anytime the rainfall rate reaches or exceeds 1 inch per hour, said Susan Cannon, a research geologist with the U.S. Geological Survey.
That's a likely scenario Wednesday in the area burned by last year's Station Fire, which charred 250 square miles above the suburbs tucked below the San Gabriel Mountains.
For all the perils of the torrential rains, there was a silver lining: The water is expected to help ease the effects of years of drought. Thursday is expected to be dry, with sunshine. There will be light rain on Christmas Day in parts of California.
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.
Contributing to this report were Associated Press writers Garance Burke in Fresno; Don Thompson in Sacramento; Sue Manning, Robert Jablon, John Antczak and Raquel Maria Dillon in Los Angeles, Felicia Fonseca in Flagstaff, Ariz., Josh Loftin in Salt Lake City, and Cristina Silva in Las Vegas.
Copyright 2010 The Associated Press.