Los Angeles - Flames raced down a steep hillside "like a freight train," leaving smouldering remains of homes and forcing thousands to flee the wildfire churning through tinder-dry canyons in Southern California, authorities said on Sunday.The fire that has destroyed at least 18 homes in northern Los Angeles County gained ferocious new power two days after it broke out, sending so much smoke in the air that planes making drops on it had to be grounded for part of the afternoon."For this time of year, it's the most extreme fire behaviour I've seen in my 32-year career," County fire Chief Daryl Osby said.About 480 kilometres up the coast, crews were battling another fire spanning more than 27 square kilometres and forcing evacuations outside the scenic Big Sur region.The Southern California blaze has blackened more than 55 square kilometres of brush on ridgelines near the city of Santa Clarita, and authorities found a burned body in a car. No new measurements were available, but officials said the fire might now be double that size.Fire 'doing what it wants'Planes were unable to make drops over the fire for a long stretch of the afternoon before resuming for a few hours before dusk. Helicopters released retardant around the perimeter of the fire all day and continued into the night."The fire's just doing what it wants right now," US Forest Service spokesperson Nathan Judy said. "We have to stick back, let it do what it wants to and attack it where we can."Juliet Kinikin said on Sunday there was panic as the sky became dark with smoke and flames moved closer to her home a day earlier in the Sand Canyon area of Los Angeles County."And then we just focused on what really mattered in the house," she told The Associated Press.Kinikin grabbed important documents and fled with her husband, two children, two dogs and three birds. They were back at home on Sunday, "breathing a big sigh of relief," she said.Residents of thousands of homes were evacuated as shifting winds were pushing flames northeast through Angeles National Forest, authorities said.Lois Wash, 87, said she and her daughter and her dog evacuated, but her husband refused."My husband's stubborn as a mule, and he wouldn't leave," Wash told KABC-TV. "I don't know if he got out of there or not. There's no way of knowing. I think the last time I looked it was about 100 metres from us. I don't know if our house is still standing or not. All we can do is pray."The fire has ripped through brush withered by days of high temperatures and years of drought."It started consuming houses that were non-defendable," Los Angeles County Deputy Fire Chief John Tripp said, describing the flames as charging through terrain "like a freight train."More than 1 600 firefighters were battling the flames that sent up a huge plume of smoke visible across the region.The body of a man was discovered on Saturday in a burned sedan outside a home in the fire zone. Los Angeles County sheriff's officials are investigating the death.Film sets destroyedThe fire destroyed film sets at Sable Ranch in Santa Clarita, which has Old West-style buildings used for movie locations. It also forced a non-profit sanctuary for rescued exotic creatures to evacuate 340 of its more than 400 animals, including Bengal tigers and a mountain lion.North on the Central Coast, a blaze consuming brush in rugged mountains near Big Sur was threatening about 1 650 homes. It burned in inaccessible terrain 8 kilometres south of Garrapata State Park and forced the communities of Palo Colorado and Carmel Highlands to evacuate, California's forestry department said.Brock Bradford lives in a historic house in Palo Colorado and could see the flames coming down the road as he evacuated."I hope I don't have to rebuild my house," he told the Monterey Herald. "I'm 66."