Authorities have warned of the threat of mudslides after a damaging storm struck California, trapping people in floodwaters, triggering a debris flow which destroyed homes and forcing residents to flee communities scorched by wildfires last year.

The powerful system swept in from the Pacific Ocean and unleashed rain, snow and wind across the US west coast into Wyoming and Colorado after walloping northern California and southern Oregon.

The rain mostly ended by Thursday evening. But officials said hillsides could still loosen and collapse, bringing down mud, boulders and debris.

“The ground is still so saturated and the water is still flowing down from the mountains,” said April Newman, spokeswoman for the Riverside County Fire Department.

The National Weather Service reported staggering rainfall amounts across California, including more than 24cm over 48 hours at one location in the San Bernardino Mountains east of Los Angeles.

California storms Show all 14 1 /14 California storms California storms Water rushes down the stairs of a house near a mudslide that destroyed three homes on a hillside in Sausalito, Calif., Thursday, Feb. 14, 2019. Waves of heavy rain pounded California on Thursday, filling normally dry creeks and rivers with muddy torrents, flooding roadways and forcing residents to flee their homes in communities scorched by wildfires. (AP Photo/Michael Short) (AP Photo/Michael Short) California storms Cars and a large tree are seen in a debris trail in the aftermath of a mudslide that destroyed three homes on a hillside in Sausalito, Calif., Thursday, Feb. 14, 2019. The National Weather Service says the atmospheric river sagged southward from Northern California overnight and is pointed at the southwestern corner of the state early Thursday. (AP Photo/Michael Short) California storms Southern Marin Fire Department members search a crushed house in the aftermath of a mudslide that destroyed three homes on a hillside in Sausalito, Calif., Thursday, Feb. 14, 2019. Waves of heavy rain pounded California on Thursday, filling normally dry creeks and rivers with muddy torrents, flooding roadways and forcing residents to flee their homes in communities scorched by wildfires. (AP Photo/Michael Short) (AP Photo/Michael Short) California storms Firefighter/paramedic Patrick Young with the Southern Marin Fire Department looks out over the aftermath of a mudslide that destroyed three homes on a hillside in Sausalito, Calif., Thursday, Feb. 14, 2019. The National Weather Service says the atmospheric river sagged southward from Northern California overnight and is pointed at the southwestern corner of the state early Thursday. (AP Photo/Michael Short) (AP Photo/Michael Short) California storms A fallen tree that was knocked down by recent severe weather lies in the Horseshoe Bay parking lot in front of the Golden Gate Bridge in Sausalito, Calif., Thursday, Feb. 14, 2019. Waves of heavy rain pounded California on Thursday, filling normally dry creeks and rivers with muddy torrents, flooding roadways and forcing residents to flee their homes in communities scorched by wildfires. (AP Photo/Michael Short) (AP Photo/Michael Short) California storms Southern Marin Fire Department members search a crushed house in the aftermath of a mudslide that destroyed three homes on a hillside in Sausalito, Calif., Thursday, Feb. 14, 2019. Waves of heavy rain pounded California on Thursday, filling normally dry creeks and rivers with muddy torrents, flooding roadways and forcing residents to flee their homes in communities scorched by wildfires. (AP Photo/Michael Short) California storms Southern Marin Fire Department members search a crushed house in the aftermath of a mudslide that destroyed three homes on a hillside in Sausalito, Calif., Thursday, Feb. 14, 2019. Waves of heavy rain pounded California on Thursday, filling normally dry creeks and rivers with muddy torrents, flooding roadways and forcing residents to flee their homes in communities scorched by wildfires. (AP Photo/Michael Short) California storms A truck drives over a flooded freeway underpass in San Francisco, Thursday, Feb. 14, 2019. The National Weather Service says the atmospheric river sagged southward from Northern California overnight and is pointed at the southwestern corner of the state early Thursday. (AP Photo/Jeff Chiu) California storms A Caltrans work crew removes debris near a flooded lane from under a freeway in San Francisco, Thursday, Feb. 14, 2019. The National Weather Service says the atmospheric river sagged southward from Northern California overnight and is pointed at the southwestern corner of the state early Thursday. (AP Photo/Jeff Chiu) California storms A Caltrans work crew removes debris near a flooded lane from under a freeway in San Francisco, Thursday, Feb. 14, 2019. The National Weather Service says the atmospheric river sagged southward from Northern California overnight and is pointed at the southwestern corner of the state early Thursday. (AP Photo/Jeff Chiu) California storms Water from recent heavy rain storms breeches a levee in Novato, Calif., Thursday, Feb. 14, 2019. Waves of heavy rain pounded California on Thursday, flooding streets, triggering a mudslide that destroyed homes and forcing residents to flee communities scorched by wildfires last year. (AP Photo/Terry Chea) California storms Water from recent heavy rain storms breech a levee and flows under railroad tracks in Novato, Calif., Thursday, Feb. 14, 2019. Waves of heavy rain pounded California on Thursday, flooding streets, triggering a mudslide that destroyed homes and forcing residents to flee communities scorched by wildfires last year. (AP Photo/Michael Short) California storms Stormy Daniels (C), the porn star who claims to have slept with US President Donald Trump over a decade ago, opens Berlin erotic fair "Venus" in Berlin on October 11, 2018. TOBIAS SCHWARZ/AFP/Getty Images) California storms A truck drives over a flooded freeway underpass in San Francisco, Thursday, Feb. 14, 2019. The National Weather Service says the atmospheric river sagged southward from Northern California overnight and is pointed at the southwestern corner of the state early Thursday. (AP Photo/Jeff Chiu)

A woman pulled from rising water in a low-lying area between those mountains and Los Angeles had a heart attack and died at a hospital, said Ryan Rolston from the Corona Fire Department. The unidentified woman was one of nine people and three dogs rescued in a flood-control channel where homeless people camp, Mr Rolston said.

A second death was reported in Escondido, northeast of San Diego, where firefighters recovered the body of a man who had been seen paddle boarding in the surging waters of a concrete-lined flood-control channel.

North of San Francisco, a mudslide barreled over cars, uprooted trees and sent a home sliding down a hill and smashing into another house in Sausalito.

A woman was rescued from the splintered wreckage with only cuts and bruises. Susan Gordon was buried under a tree and mud for two hours while crews dug her out, her son wrote on an online fundraising page.

Chris Parkman said it has been years since a storm so powerful has hit the hillside community, where at least 50 properties were evacuated.

“We don’t see the rain most of the year. So most of the year you feel safe. But when the big storms come, your safety factor is gone,” he said.

Further north, a levee along State Route 37 near Novato was breached, flooding a rural field. Officials were monitoring the area in case water flowed onto the highway or train tracks.

A deluge southeast of Los Angeles washed away a section of a two-lane mountain highway. Photos by the state Department of Transportation showed about 23 metres of pavement completely collapsed along State Route 243 near the remote community of Idyllwild.

“We’re basically stranded right now,” said resident Gary Agner, adding that several other roads were closed because of flooding and debris. “I’m glad I went to the grocery store yesterday.”

The risk of flooding led officials to order people out of areas burned bare by a summer wildfire in the Santa Ana Mountains, with flash-flood warnings blanketing a huge swath east and south of Los Angeles. The evacuation orders were downgraded to flood warnings by Thursday night.

Authorities also told parts of Laguna Beach to evacuate for much of the day, while the desert resort city of Palm Springs urged residents to stay where they were because of flooded streets. Flood advisories extended to Arizona.

Weather was so severe that the Hollywood Walk of Fame had to postpone the dedication of a sidewalk star honoring the band Aerosmith. Knott’s Berry Farm and Six Flags Magic Mountain theme parks closed.

Trouble also persisted in saturated northern California, where thousands of people lost power and flooding was possible. Downtown San Francisco saw more than 4 centimetres of rain over 24 hours.

A flooded creek led authorities to urge about 300 residents to leave a community about 20 miles west of Paradise, a town destroyed last year by the nation’s deadliest wildfire in a century.

The storm followed more than a week of severe weather in the Pacific Northwest and was the latest in a series of storms that has all but eliminated drought-level dryness in California this winter. It’s fueled by an atmospheric river – a plume of moisture stretching across the Pacific Ocean nearly to Hawaii.

Nearly 37 per cent of California had no level of drought or abnormal dryness, the US Drought Monitor reported on Thursday. About 10.5 per cent of the state was in moderate drought, and just over 1.6 per cent was in severe drought. The remainder was in the abnormally dry category. The numbers reflect data gathered up to Tuesday.

Atmospheric rivers are long bands of water vapor that form over an ocean and flow through the sky. Formed by winds associated with storms, they occur globally but are especially significant on the west coast.

Even before the height of the storm, mandatory evacuations were ordered near the wildfire area in the Santa Ana Mountains where officials said there was a high risk of debris flows.

Tim Suber chose not to leave his hillside neighborhood in Lake Elsinore. He said he has lost count of how many times his family has been evacuated between last summer’s devastating wildfire and this winter’s storms.

The rain was so heavy that “it sounds like a hundred bowling balls a minute are going down the creek” behind his house, Mr Suber said. A neighbour had mud in his pool, but so far the area hadn’t lost power and culverts and washes were handling the runoff.

The storm delayed flights destined for San Francisco International Airport, closed sections of several key highways, including Highway 1 on the Central Coast, Interstate 5 north of Sacramento, and US 395 in the snowy eastern Sierra Nevada.

Wintry weather closed Interstate 80 in California near the Nevada border and across much of Wyoming and sections of at least four other highways. Multiple avalanches disrupted highway traffic in northwestern Montana near the Idaho border.

In Colorado, high winds shattered windows and downed power poles, leaving thousands in Colorado Springs without power.