LOS ANGELES >> A storm of historic proportions dumped a record amount of rain over parts of Los Angeles today, 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.

About 830,000 people statewide were without power Monday afternoon.

The storm was the second one fueled by an atmospheric river to hit the state over the span of days.

Virtually all of Southern California was under flash flood advisories and watches, including the Los Angeles area, where between 5 and 10 inches (12.7 to 25.4 centimeters) of rain had fallen and more was expected, according to the National Weather Service.

So far officials have attributed three deaths to the storm that first hit Northern California. Crews were rescuing people from swift-moving water in various parts of Southern California on Monday.

Among those rescued were two homeless people who spent the night on a small island in the Santa Ana River in San Bernardino, about 55 miles (88.51 kilometers) east of Los Angeles, authorities said.

“They were cold and exhausted from a night out stranded on this little patch of dirt that was in the middle of the river,” said Capt. Nathan Lopez of the San Bernardino County Fire Department. A dog and two cats were also saved.

Near the Hollywood Hills, floodwaters carried mud, rocks and household objects downhill through Studio City, damaging at least two homes, city officials said. Sixteen people were evacuated.

“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.

Drake Livingston who lives in the Beverly Crest neighborhood, was watching a movie around midnight when a friend alerted him to flooding.

“We looked outside and there’s a foot-and-a-half of running water, and it starts seeping through the doors,” said Livingston, whose car was found submerged in several feet of mud in the morning.

Los Angeles Mayor Karen Bass urged residents to avoid driving, warning of fallen trees and electrical lines on flooded roadways.

It was already the third wettest two-day period on record in downtown Los Angeles as of Monday afternoon and some was still coming down, said Dave Bruno, meteorologist with the National Weather Service, Los Angeles. The area was also on par to get about half its annual rainfall in one storm. The service has been keeping records in downtown since 1877.

“This is something that will be remembered, just based on numbers, for a while,” Bruno said.

Shelters were adding beds for the city’s homeless population of nearly 75,000 people.

Tony Sanz spent the night in a city park before seeking higher ground around dawn as floodwaters were rising around his tent.

“Boy did it rain last night,” he said Monday afternoon hunkered down in a tent layered with tarps on a sidewalk outside a supermarket. He spied the cloudy skies during a break in the downpours and wondered, “Is that it? I hope that’s it.”

The weather service forecast up to 8 inches (20 centimeters) of rainfall across Southern California’s coastal and valley areas, with 14 inches (35 centimeters) possible in the foothills and mountains over the next two days.

Amid storm conditions about 1 million gallons of untreated sewage was released into the Pacific Ocean. In response, Los Angeles County health officials blocked access to the ocean off popular Cabrillo Beach near the Port of Los Angeles.

Earlier in the day, commuters stepped through several inches of floodwater as they rushed to catch trains at Union Station in downtown Los Angeles.

Most Los Angeles public schools remained open but some districts were closed. The weather also prompted a rare early closure of Disneyland.

Over the weekend, the storm inundated streets and brought down trees and prompted water rescues in the San Francisco Bay area.

Among those who died were two men killed by fallen trees Sunday in Carmichael, a suburb of Sacramento, and in Boulder Creek in. Police were investigating the death of another man in Yuba City, about 100 miles (160 kilometers) northeast of San Francisco, who was found under a big redwood tree in his backyard Sunday.

Gov. Gavin Newsom declared a state of emergency for most of coastal Southern California, while emergency shelters were opened.

Off the coast of Long Beach, 19 people were rescued Sunday after the 40-foot sailboat they were traveling in lost its mast amid gale-force winds, said Brian Fisk of the Long Beach Fire Department.

Heavy snow was falling throughout the Sierra Nevada and motorists were urged to avoid mountain roads.

Much of the state was still drying out from the initial atmospheric river-powered storm that blew in last week. 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.

Both atmospheric rivers were called a “Pineapple Express” because they originated near Hawaii.

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. Nine were categorized as strong, two were extreme and one was exceptional.