The extreme weather that has battered southern California in recent days, unleashing record amounts of rain and causing hundreds of mudslides, was expected to ease as the storm moves out of the region on Wednesday.

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Authorities continued to warn that the threat of collapsing hillsides remains after the historic storm, one of the wettest ever seen in southern California.

The wet weather has dumped over 1ft of rain in the region, caused 475 mudslides around Los Angeles, and downed 400 trees. Across the state, at least seven people died. The storm is projected to have caused as much as $11bn in damage and economic losses, according to a preliminary estimate from Accuweather.

The weather began to relent on Tuesday and evacuation orders were lifted for homes in flood- and slide-prone areas. But with a heavy cloudburst forecast for Wednesday afternoon, a flood watch for Los Angeles county was extended until Wednesday afternoon, a flash-flood warning was posted for the Orange county coast, and flood advisories were issued as far south as San Diego and the US-Mexico border.

It would not take much for water, mud and boulders to sluice down fragile hillsides, experts warned.

“The ground is fully saturated and simply cannot hold any more water” even if rains are light, the National Weather Service meteorologist Tyler Kranz said.

On Tuesday, Dion Peronneau in the Los Angeles suburb of Baldwin Hills was trying to get her artwork and books out of her house. Mud knocked her sliding glass doors off their frame and poured into her home of 25 years.

“Eight feet of mud is pressed up against my window that is no longer there,” she said. “They put up boards to make sure no more mud can come in.”

Karen Bass, the Los Angeles mayor, said the city was looking toward helping people recover from the weather’s pounding. Officials will seek federal emergency money to help move homeless people out of shelters and to aid owners of damaged hillside homes where insurance companies would not cover the losses, she said.

Work crews, meanwhile, struggled to deal with the storm’s aftermath. Thousands of customers remained without power late on Tuesday, after rain flooded electrical vaults and trees brought down on power lines. Across the state, more than 70,000 homes and businesses remained without power on Wednesday morning.

People were being urged to avoid touching the lines for fear of electrocution and to steer clear of roadways at risk of floods and mud. Over the course of the storm, dozens of people in Los Angeles alone – including at least 50 stranded motorists – were rescued from fast-moving, swollen creeks, rivers, roads and storm channels, fire officials said, as well as several animals.

Officials warned residents to stay out of flooded areas and avoid driving into mountainous areas where there is ongoing risk for rockslides and mudslides due to the wet weather.

Further north, in Isla Vista, several people were evacuated and dozens displaced after the cliff their homes were built on had begun to erode. Authorities in the area warned residents to stay away from the edges of bluffs as heavy rain can cause erosion.

Related: California flooding: how atmospheric rivers led to a state of emergency

The stormy weather first hit northern California over the weekend before moving south and inundating southern California for days. Seven storm-related deaths were reported across the state, including four people crushed by toppling trees and someone who was swept up on Tuesday in a swollen Tijuana River channel near the border with Mexico, immigration officials said.

The California highway patrol said a 69-year-old man died on Monday after his truck went down an embankment and filled with water in Yucaipa, about 80 miles (128km) east of Los Angeles.

The weather has been particularly harrowing for the state’s large unhoused population. A 73-year-old Sacramento woman had to be cut out of her tent after a tree toppled over and destroyed her shelter.

“I just went out three days ago and bought this tent with my only paycheck,” the woman told the Sacramento Bee. “I’m going to have to save two more months to get another tent.”

In Los Angeles, where there are more than 75,000 unhoused people, the city said on Tuesday that its winter shelters were almost completely full.

All the rain brought one silver lining: helping to boost the state’s often-strapped water supply. At least 6bn gallons (22.7bn liters) of storm water in Los Angeles alone were captured for groundwater and local supplies, the mayor’s office said.

The latest storms followed a string of atmospheric rivers that pummeled the state last year, leading to at least 20 deaths.

As the latest weather front moved east, it prompted warnings across the state line.

Parts of northern Arizona stretching south-east toward New Mexico were under a winter storm warning through 5pm local time on Wednesday and a wide swath of west-central Arizona, including Phoenix, remained under a flood watch until Thursday morning.