LOS ANGELES -- A storm of historic proportions dumped a record amount of rain over parts of Los Angeles on Monday, sending mud and boulders down hillsides dotted with multimillion-dollar homes while people living in homeless encampments in many parts of the city scrambled for safety.
More than 1 million people statewide were without power.
The storm was the second one fueled by an atmospheric river to hit the state over the span of days.
About 2.5 million people in the Los Angeles area, including the Hollywood Hills and Beverly Hills, were under a flash flood warning. Up to 9 inches of rain had already fallen in the area, with more expected, according to the National Weather Service, which called the flash flooding and threat of mudslides "a particularly dangerous situation."
Already crews were rescuing people from swift-moving water in various parts of Southern California, including two homeless people who were evacuated Monday from a small island in the Santa Ana River in San Bernardino, about 55 miles east of Los Angeles, authorities said.
Gushing rivers carried mud, rocks and household objects downhill as floodwaters coursed through Studio City, an area on the back side of the Hollywood Hills.
Sixteen Studio City residents were evacuated and two homes were damaged, city officials said.
"It looks like a river that's been here for years," said Keki Mingus, whose neighbors' homes were damaged. "I've never seen anything like it."
The Los Angeles Fire Department said 1,000 firefighters were contending with 49 debris flows, 130 reports of flooding, half a dozen structure fires and several rescues of motorists stranded in vehicles.
Los Angeles Mayor Karen Bass urged residents to avoid driving, warning of fallen trees and electrical lines on flooded roadways.
More than 10 inches of rain has fallen in the Santa Monica Mountains. Los Angeles Fire Chief Kristin Crowley said hazards will continue to be a threat in areas around recent wildfire burn scars, noting that rain is forecast to continue today.
A record 4.1 inches of rain fell Sunday in downtown Los Angeles, making it the 10th-wettest day on record, the National Weather Service said. That's more rain than the area typically gets for the entire month.
The weather service forecast up to 8 inches of rainfall across Southern California's coastal and valley areas, with 14 inches possible in the foothills and mountains over the next two days.
Commuters stepped through several inches of floodwater Monday morning as they rushed to catch trains at Union Station in downtown Los Angeles.
The storm over the weekend inundated streets and brought down trees and electrical lines throughout the San Francisco Bay Area, while the weather service issued a rare "hurricane-force wind warning" for the Central Coast. Several people had to be rescued from rising floodwaters, including those in cars and others living in homeless encampments.
In Yuba City, about 100 miles northeast of San Francisco, police said they were investigating the death of a man found under a big redwood tree in his backyard Sunday evening. A neighbor heard the tree fall, and it was possible the man was using a ladder to try and clear the redwood when he was killed, police said on Facebook.
In Southern California, off the coast of Long Beach, 19 people were rescued Sunday after the 40-foot sailboat they were traveling in lost its mast, said Brian Fisk, a firefighter and paramedic for the Long Beach Fire Department.
Another vessel heard the distress call on the marine radio and helped rescue eight people while 11 were able to get onto the rocky breakwater by Alamitos Bay where they were rescued by lifeguards, he said. One person was treated for injuries.
"They went out sailing in gale-force winds and stormy weather," Fisk said. "They're very, very lucky."
Gov. Gavin Newsom declared a state of emergency for most counties in coastal Southern California and said emergency resources were ready, while emergency shelters were opened.
Atmospheric rivers are relatively narrow plumes of moisture that form over an ocean and can produce torrential amounts of rain as they move over land.
Since last winter, 46 atmospheric rivers have made landfall on the U.S. West Coast, pulling the state out of a yearslong drought, according to the Scripps Institution of Oceanography's Center for Western Weather and Water Extremes.
Information for this article was contributed by Michael R. Blood, Eugene Garcia and Amy Taxin of The Associated Press.