Residents tie the axle to a large tree to secure a van caught in a flooded area in Silverado Canyon, Calif., on Wednesday. ((Alex Gallardo/Associated Press))

A powerful storm dumped more rain on already waterlogged Southern California on Wednesday, washing hillsides onto highways, endangering houses in canyons and forcing rescuers to pluck dozens of motorists from flooded streets.

The storm was expected to ease as it moved eastward. Floodwaters washed away homes in Arizona, and inundated parts of Nevada and Utah.

The low-pressure system could be in New Mexico by Thursday and could reach the Gulf Coast by Saturday with some rain, but not the deluge that hit Southern California, forecasters said.

In Southern California, the burst of heavy rain in the morning left streets flooded and caused minor mudslides. The threat, however, of larger mudslides could last for weeks in the suburban Los Angeles canyon hillsides laid bare 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.

Spencer added that catch basins designed to hold a landslide's uprooted trees and other debris before it can wash down onto homes appeared to have plenty of capacity.

Heavy rains early Wednesday caused a hillside to collapse on part of a busy Interstate 10 transition road about 48 kilometres outside Los Angeles.

In eastern Orange County, 25 to 30 people were evacuated from their homes in Silverado Canyon. The houses were threatened by rolling boulders and debris flow. The canyon is on the edge of the Cleveland National Forest that burned in a 1997 wildfire.


A worker removes a large tree from a home on Oletha Lane in the Beverly Glen neighbourhood of Los Angeles on Tuesday. ((Jason Redmond/Associated Press))

Silverado Creek was swollen with muddy brown water and roads were choked with mud and uprooted trees.

Orange County Fire Authority Capt. Larry Kurtz said firefighters walked residents to a church and searched deeper in the canyon for remote homes. "If we have any more rain, there are people who just can't get out," Kurtz said.

Paul Wright, whose best friend died in an Orange County mudslide in 1997, said he was awakened by the sound of rolling boulders at 3 a.m. and hurried to get his family out of his home.

"There's huge, big boulders, 'Boom! Boom!' " he said. "I lost my house in the Laguna mudslide, so I'm erring on the side of caution."

Wright and his dog, Joe, waited outside a grocery store to be evacuated. Wright said he hoped to join his wife and two young children who already fled to a nearby church.

Some residents refused to leave.

Rick Tallant said he has lived in the canyon for nine years and planned to wait out the rain at his home.

"I didn't leave during the fire three years ago and I'm not going to leave now just because it's wet," he said. "I'm probably just going to go home and sit and stay dry."

In the towns of Laguna Beach and adjoining Laguna Woods, rescuers plucked more than 30 drivers, pedestrians and people stuck in their homes as mud and stormwater poured down steep hillsides.

"There's mud and rocks and hillside collapses," Laguna Beach police Lt. Jason Kravetz said. "It was too much (rain), too quick."

One man was rescued from his house after a mudslide pushed in one of the walls, he said.

An area in Laguna Beach, including downtown, was closed as up to 1.2 metres of water rolled down the streets from Laguna Creek. The water later receded but left a mushy carpet of mud.

Officials on Tuesday ordered the 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.

The area is where the Station Fire charred more than 647 square kilometres above suburbs tucked below the San Gabriel Mountains.