(CNN) Heavy rains unleashed destructive rivers of mud and debris in Southern California on Tuesday -- leaving at least 13 people dead, destroying homes and spurring rescues as the flooding forced heavily traveled roads to close.

Santa Barbara County Sheriff Bill Brown said the death toll could rise. Officials said many of the deaths are believed to be in the coastal Montecito area, where mudflows and floodwater have inundated areas downstream from where the Thomas Fire burned thousands of acres last month.

At least two dozen people were unaccounted for and authorities rescued at least 50 people in the Montecito area. The Santa Barbara Sheriff's Department is working toward determining whether those "missing" were accounted for in other locations or among those who are deceased.

"It looked like a World War I battlefield," Brown said of the destruction. "It was literally a carpet of mud and debris everywhere, with huge boulders, rocks, down trees, power lines, wrecked cars -- lots of obstacles and challenges for rescue personnel to get to homes."

Latest developments

• Thirteen storm-related deaths were reported in Santa Barbara County, Sheriff Brown said.

• The 101 Freeway in parts of Montecito and Santa Barbara, will remain closed for at least 48 hours after muddy, debris-filled water flooded parts of the seaside roadway, according to Capt. Cindy Pontes with the California Highway Patrol.

• By early Tuesday afternoon, more than 5.5 inches of rain had fallen in parts of Ventura County over two days, the National Weather Service said. In Carpinteria, nearly 1 inch fell in just 15 minutes, the agency said.

Check out this mudslide blocking NB lanes of 101 between Carpenteria and Montecito. The highway is closed from Ventura to Santa Barbara. pic.twitter.com/idt5nmntbx — Leah Pezzetti (@leahpezzetti) January 9, 2018

• The weather forced the closure of several theme parks, including Six Flags Magic Mountain in Valencia and SeaWorld in San Diego.

Photos: Deadly mudslides in Southern California An aerial view of Montecito, California, shows mudflow and debris on Wednesday, January 10, 2018. Heavy rains unleashed deadly mudslides Tuesday that damaged or swept away dozens of homes in Southern California. Hide Caption 1 of 18 Photos: Deadly mudslides in Southern California A damaged home is seen in Montecito on January 10, 2018. Hide Caption 2 of 18 Photos: Deadly mudslides in Southern California Part of a structure sits in a tree after being knocked off its foundation by a Montecito mudslide on January 10, 2018. Hide Caption 3 of 18 Photos: Deadly mudslides in Southern California Emergency personnel carry a woman from a collapsed house after a mudslide in Montecito on January 9, 2018. Hide Caption 4 of 18 Photos: Deadly mudslides in Southern California Kerry Mann navigates the large boulders and mudflow that destroyed her friend's home in Montecito. Hide Caption 5 of 18 Photos: Deadly mudslides in Southern California A view of the 101 freeway from Olive Mill Road in Montecito. Hide Caption 6 of 18 Photos: Deadly mudslides in Southern California Phillip Harnsberger crosses through mud from a flooded creek in Montecito on January 9, 2018. Hide Caption 7 of 18 Photos: Deadly mudslides in Southern California Mud fills the interior of a destroyed car in Burbank on January 9, 2018. Hide Caption 8 of 18 Photos: Deadly mudslides in Southern California Runoff water from a creek floods Highway 101 in Montecito on January 9, 2018. Flooding forced many heavily traveled roads to close. Hide Caption 9 of 18 Photos: Deadly mudslides in Southern California Reilly, a search dog with the Santa Barbara County Fire Department, looks for victims in Montecito on January 9, 2018. Hide Caption 10 of 18 Photos: Deadly mudslides in Southern California A firefighter clears debris in Los Angeles on January 9, 2018. Hide Caption 11 of 18 Photos: Deadly mudslides in Southern California A van is stuck in the mud in the Sun Valley neighborhood of Los Angeles on January 9, 2018. Hide Caption 12 of 18 Photos: Deadly mudslides in Southern California A police vehicle drives across a flooded side road in Montecito, near the San Ysidro exit of Highway 101 on January 9, 2018. Hide Caption 13 of 18 Photos: Deadly mudslides in Southern California Mud covers a road in Burbank on January 9, 2018. Hide Caption 14 of 18 Photos: Deadly mudslides in Southern California Los Angeles firefighters work amid floodwaters and mud on January 9, 2018. Hide Caption 15 of 18 Photos: Deadly mudslides in Southern California A member of the Long Beach search and rescue team looks for survivors in a car in Montecito on January 9, 2018. Hide Caption 16 of 18 Photos: Deadly mudslides in Southern California Mud washes away personal belongings in the Sun Valley neighborhood of Los Angeles on January 9, 2018. Hide Caption 17 of 18 Photos: Deadly mudslides in Southern California Rushing rainwater fills the Los Angeles River near downtown Los Angeles. Hide Caption 18 of 18

'Call after call' from stranded residents

Before the storm hit, Santa Barbara issued mandatory evacuations for more than 6,000 people, including living in those parts of Carpinteria, Montecito and Goleta, located below areas scorched by wildfires, including the Thomas Fire, county spokeswoman Gina DePinto said.

Voluntary evacuation warnings were in effect for another 20,000 people, including others in those same communities, she said.

Brown said deputies and search and rescue team members went door-to-door Monday conducting evacuations in the mandatory evacuation areas. Those notifications were all made by nightfall, Brown said.

"While some residents cooperated with the evacuations, many did not. Many chose to stay in place, "Brown said.

The sheriff said the storm hit hard around 3 a.m. Tuesday. Between 3 and 6 a.m., dispatchers with the sheriff's office handled more than 600 telephone calls for assistance.

"They received call after call from people who were distressed, stranded in their homes or vehicles and were in need of immediate rescue," Brown said.

He added: "Once daylight came, we had a very difficult time assessing the area and responding to many of those areas to assist those people."

Brown said the mud was "knee-deep" in many places on the roadways and even deeper in the canyons.

A tractor trailer in Southern California is stuck in mud and debris.

Teenager trapped for hours in Montecito

The rain fell in areas charred by recent wildfires, triggering warnings of flash flooding and mudslides because vegetation that otherwise would hold hills together and make the terrain flood-resistant has burned away.

In Montecito, six homes were "wiped away from their foundations" by mudflow and debris, Santa Barbara County fire spokesman Mike Eliason said.

Eliason said firefighters rescued a 14-year-old girl, who had been trapped for hours in a collapsed Montecito home. The girl, coated head to foot in mud, was led by firefighters from the pile of wood and debris that was once a house, a photo from the county fire department shows.

Firefighters lead a girl, 14, from the rubble where she'd been trapped for hours Tuesday in Montecito.

In another part of Montecito, Eliason said he saw "utter devastation."

"There were three houses that were completely knocked off their foundations. Debris and wood everywhere, looking like matchsticks," he said.

Eliason recalled looking at the red band on a radar, indicating heavy rainfall.

"When that hit those hillsides, it just came rushing down," Eliason said. "Time and time again, I found myself waist deep in floodwater.

The mud and debris left roadways and neighborhoods in Montecito unrecognizable.

View from the air in Montecito. Areas that had been roadways, driveways, and homes, are now unrecognizable due to the large amount of mud and debris flows. pic.twitter.com/dbsUPw3mrL — VenturaCoAirUnit (@VCAirUnit) January 9, 2018

'Mud came in an instant, like a dam breaking'

Ben Hyatt said a river of mud had crashed through a neighbor's house in Montecito, a community of about 8,000 east of Santa Barbara,

"Apparently, one of their cars ended (up) in their backyard. We have neighbors at (the) top of the street that evacuated to their roof," Hyatt said.

Hyatt said his Montecito house was "surrounded by mud," and a washing machine had drifted into his front yard.

Debris litters the area near Hyatt's home Tuesday in Montecito in Santa Barbara County.

Hyatt said he was awake when power went out during heavy rain around 2:30 a.m. Eventually, he heard a loud swish and banging on the exterior of his house.

"Mud came in an instant, like a dam breaking. (It) surrounded the house, 2 to 3 feet," he said.

"Seems calm now. We feel safe. But definitely stuck here for a bit."

This in front of the @FSSantaBarbara above #butterflybeach. Debris from our neighborhood no doubt. pic.twitter.com/IMa3Iypb1s — Benjamin Hyatt (@caffeineben) January 9, 2018

There were several glimmers of hope, as emergency officials rescued stranded residents.

Victim who was swept away in their vehicle was located by the crew of AirSquad6. Victim was hoisted and flown to awaiting ground personnel. pic.twitter.com/RvX743x0yi — VenturaCoAirUnit (@VCAirUnit) January 9, 2018

Eliason, the Santa Barbara County fire spokesman, posted photos of firefighters leading people through mud and floodwater to safety.

#CAstorm- Santa Barbara county FF's rescue two men and a woman from flood water/debris flow of Hot Springs Rd. in Montecito. Multiple rescues are underway throughout the area. pic.twitter.com/bT5WAoAvf8 — SBCFireInfo (@EliasonMike) January 9, 2018

Also in Montecito, a ruptured gas line led to a fire that consumed a building, Eliason said.

Surveillance camera video appears to show an explosion connected to that fire, said Eric Trautwein, who posted the footage on Twitter.

This is security cam footage of the explosion in #montecito pic.twitter.com/gXj6as7N8S — Eric P Trautwein (@EricPTrautwein) January 9, 2018

Cars mired in the muck

Photos of vehicles stuck in mud in Los Angeles County and nearby areas dotted Twitter feeds. One post showed a California Department of Transportation crew trying to help a trapped motorist.

In another, a Los Angeles police squad car was mired in the muck. "Officers were responding to help with evacuations. Within seconds their vehicle was consumed by the mud," the post reads.

The #LARain Is Moving Fast. Officers were responding to help with evacuations. Within seconds their vehicle was consumed by the mud. All officers are safe. pic.twitter.com/qJzJFvNoT9 — LAPD HQ (@LAPDHQ) January 9, 2018

'Praying' for Santa Barbara

Oprah Winfrey, who has home in Montecito, said she was "praying for our community again in Santa Barbara."

"Woke up to this blazing gas fire," she posted on social media.

Winfrey also showed photo of mud in her backyard.

"Helicopters rescuing my neighbors. Looking for missing persons. 13 lives lost," she wrote.

More than 1 inch of rain per hour

What's a mudflow? Heavy rains make Southern California vulnerable to flooding and debris flows, especially after fires that strip steep hillsides of vegetation. Mudflows, mudslides and landslides often are used interchangeably when disaster strikes, but the terms have distinctions. A mudflow is "a river of liquid and flowing mud on the surfaces of normally dry land areas," according to the Federal Emergency Management Agency. "Other earth movements, such as landslide, slope failure or a saturated soil mass moving by liquidity down a slope, are not mudflows," it says. FEMA sees a mudflow as similar to a milkshake, while the more solid mudslide is comparable to a cake. The US Geological Survey dismisses mudslide as an "imprecise but popular term ... frequently used by laymen and the news media to describe a wide scope of events, ranging from debris-laden floods to landslides." A landslide occurs when soil or rock moves downhill, usually due to gravity, but erosion, heavy rains and earthquakes can contribute to landslides. Sources: FEMA, US Geological Survey

The rainfall rate of more than 1.5 inches per hour in parts of Southern California overwhelmed the landscape.

About a half inch per hour is enough to start mudslides, said Robbie Monroe of the National Weather Service in Oxnard.

The downpour is overpowering a terrain especially vulnerable in the wake of recent fires.

The Thomas Fire -- the largest wildfire in California's recorded history -- has burned more than 281,000 acres in Santa Barbara and Ventura counties since it began in early December. It was 92% contained, and officials don't expect full containment until later this month.

Montecito and Carpinteria are vulnerable to mudslides because the steep terrain in some places goes from thousands of feet above to sea level to sea level in "a matter of just a few miles," said Tom Fayram, a deputy public works director with Santa Barbara County

"That's definitely at play here. It's just a mess," he said.

Fayram said crews working to clear mud and debris from roadways saw "boulders the size of trucks that came rolling down the hillsides."

"This is a disaster, much worse than the mudslides of 1995," Fayram said. We're trying to get help from federal and state officials."

The region has suffered from years of drought, and officials say they need the rain to regrow plants and trees that help keep the hillsides together and floodproof.

Rainfall and mudflow damaged guest cottages at the San Ysidro Ranch in Montecito, California.

Mudslides are not uncommon to the area and can be deadly.