Hiker is critically injured by boulder; mudslides hit Hollywood Hills and Echo Park

The latest in a series of winter storms that have hammered Southern California for days sent soil sliding from beneath a house in the Hollywood Hills, forcing evacuations, and a boulder tumbling down a hillside in Malibu, leaving a hiker critically injured.

The 57-year-old woman was pummeled by the large boulder Thursday on Rambla Pacifico Street, the Los Angeles County Sheriff’s Department said.

No one was injured in the Hollywood Hills slide, but fire officials evacuated five workers from the home, which is under construction above Stanley Avenue, along with residents of about 20 surrounding homes, for several hours.

Four of those homes were yellow-tagged; authorities told those residents they could go home but must stay out of their backyards. Geologists will assess the area for potential danger, Los Angeles Fire Department spokesman Brian Humphrey said.

In Echo Park, a fourplex was red-tagged — meaning no one can go inside — when its staircase collapsed, causing soil and debris to slam into two parked cars, he said.

By 8:30 p.m., the Fire Department was on its “1,800th incident today,” Humphrey said. “Every single one has some nexus to the rain.… It’s been a very busy day.”

Bands of heavy precipitation that moved into L.A. early Thursday from an “atmospheric river” — a long plume of water vapor pouring over from the Pacific Ocean and swollen with subtropical moisture — also wreaked havoc on roadways, causing dozens of crashes, including an overturned car that blocked several lanes on the southbound 110 Freeway in Highland Park.

A flooded tunnel closed a portion of the northbound 101 Freeway near the East Los Angeles interchange downtown shortly after 5 a.m., and a stretch of Topanga Canyon Road was cordoned off after boulders and mud slid from the hillside onto the roadway. A massive boulder that fell into the roadway briefly closed Stunt Road in Calabasas between Mulholland Highway and Schueren Road.

In Ventura County, about 50 people were evacuated from an RV resort near the 101 Freeway just before floodwaters from the Ventura River inundated the property. Muddy water that pooled in the resort’s parking lot rose to the top of the doors of two trucks and an SUV that had been left behind.

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Firefighters respond to mudslide in Hollywood Hills.

The National Weather Service warned that periods of heavy rain could trigger shallow mud and debris flows in areas recently devastated by wildfires.

The soil in burn areas cannot absorb a lot of moisture, so heavy rainfall can lead to fast-moving flows containing mud, debris and even trees and boulders. When rain falls over time, it can be gradually absorbed or dispersed, but when areas see rapid runoff, entire hillsides can come down without warning, sometimes with deadly results.

Riverside County officials issued mandatory evacuations for several communities near the Holy fire burn area. They were lifted and made voluntary at about 6 p.m. Thursday. Debris flows and flooding in the area closed a portion of Temescal Canyon Road shortly after 11:30 a.m.

Previous flood alerts in Ventura and Los Angeles counties expired as rainfall lessened in those areas, and residents of 300 homes in the Woolsey fire burn area were allowed to return home. Malibu schools were closed for a third consecutive day because of the rain but were scheduled to reopen Friday.

The storm, which moved into the region Wednesday, was expected to dump from 1½ to 3 inches of rain along the coast in Ventura and Los Angeles counties through Thursday evening. The foothills could see up to 5 inches of precipitation by the time the rain tapered off, forecasters said.

Much of Southern California had already received a heavy soaking. By 10 a.m., about 1.79 inches of rain had fallen on downtown Los Angeles in a 24-hour period, while Nordhoff Ridge in Ventura County had been hammered with 6.88 inches — the most in the region. A storm cell that hovered over Seal Beach late Wednesday dropped more than 3 inches and caused roads and a beach parking lot to flood. A stretch of Pacific Coast Highway in Huntington Beach also remained closed after the road flooded on Wednesday.

Heavy rain also forced the closure of Knott’s Berry Farm and Six Flags Magic Mountain. Disneyland and Universal Studios remained open.

The series of storms also knocked out power for thousands of people throughout the state. Pacific Gas and Electric said about 68,000 customers in Northern California remained in the dark Thursday, down from 220,000 the previous day. Southern California Edison reported about 2,000 customers without power.

Thursday’s precipitation was the final punch in nearly a week of wet weather across the state, and the rains could signal movement in the right direction for California’s lackluster water supply, said retired climatologist Bill Patzert.

“The big picture is that really for the last two decades, we’ve mostly been in a rain-deficit situation, so the result of course is that groundwater basins all over California are extremely low,” he said. “Coming into this winter we are rain-needy.”

Meteorologists said the storm brought blizzard conditions to the higher elevations of the Sierra Nevada with several feet of fresh snow and winds surpassing 50 mph. Heavy overnight snowfall upended a Citation X Cessna airplane at Truckee Tahoe Airport, leaving the nose pointed upward for several hours.

The state’s rainy season — which lasts through March — consists of about 10 storms, on average, Patzert said. This series of unusual back-to-back events has put California ahead of schedule in terms of rain, which could signal positive steps to replenishing the state’s depleted reservoirs, he said.

“It took us years to get into this water deficit, and it will take us years to get out,” he said. “This is several days of sweet rainfall, but it’s no solution. It’s a good start.”

The Associated Press contributed to this report.

hannah.fry@latimes.com

Twitter: @Hannahnfry