A huge storm system has dumped record amounts of rain on southern California and prompted concern that the poor weather could spread across the US.
Streets flooded, residents were evacuated and authorities were on alert for landslides in the wake of the torrential downpour.
The deluge came at the end of a week that saw Los Angeles receive half its annual rainfall in just six days.
Torrential rain was also reported in neighbouring Arizona, Nevada and Utah.
There are concerns that the weather system will spread across the US, reaching New Mexico by Thursday and the Gulf Coast by the end of the week.
However, forecasters said the rain would ease as it travelled eastwards.
Even before the storm arrived, Governor Arnold Schwarzenegger declared a state of emergency for half a dozen communities in California, some of which have already seen mudslides and flooded streets.
Hundreds of people were evacuated in the suburbs of Los Angeles, with particular concerns for homes in steep-sided canyons previously ravaged by wildfires.
"The ground is so saturated it could move at any time," said Bob Spencer, spokesman for the Los Angeles County Department of Public Works.
There were reports of mudslides in Laguna Beach, California, as intense rain hit the region, and 25 to 30 people were evacuated from their mountain homes in Silverado Canyon, Orange County, the Associated Press reported.
Heavy rains - estimated at up to 1in (2.5cm) per hour - brought down a hillside on a heavily used section of Interstate 10 early on Wednesday, covering three lanes near the city of Pomona.
In Highland, some 65 miles (104km) east of Los Angeles, two creeks overflowed, swamping as many as 20 homes in mud.
"This mud flow moved cars, picked them up, stood them up on their nose at 45-degree angles, buried them," Bill Peters, a spokesman for the California department of forestry and fire protection told AP.
Homes in the mountains were blocked by boulders and mud as rescue workers helped residents seek shelter before the largest of the storms struck.
In far north-western Arizona, residents rushed to gather belongings from their homes along a flooded stretch where further structures risked being swept away.
"It is a mess," said Lois Rolfsmeyer, resident of Beaver Dam.
"The water is going to take our next-door neighbour's house and the one behind us, and it's eroding under our house."
On Tuesday, officials ordered the evacuation of 232 homes that sit beneath large hillsides in La Canada Flintridge and La Crescenta, in the suburbs of Los Angeles.
Flood warnings and emergency orders have also been put in place in Arizona, Nevada and Utah.