A brief but fierce cloudburst sent mud, water and large rocks flowing from slopes denuded by wildfire into a foothill neighborhood north of Los Angeles, authorities said Friday.
Homeowners said debris from San Gabriel Mountain slopes began flowing shortly before 11 p.m. Thursday.
Residents of about a dozen homes fled, but there was no official evacuation and no injuries were reported, fire officials said.
Crews used skiploaders, dumptrucks, shovels and wheelbarrows to clear a thick layer of mud from the backyards of several homes along steep and winding streets.
Some cars were partially buried and rocks the size of soccer balls briefly made a road impassable, Los Angeles County fire Battalion Chief Steve Martin said.
A half-dozen homes were slightly damaged when mud and water oozed over their floors, fire officials said.
Several feet of mud topped concrete barriers on Rock Castle Drive that had been put in place specifically to protect homes.
Gary Stibal, who has lived in the neighborhood since 1973, found his backyard buried under about five feet of mud that pressed up against the rear of his home, flush with the top of a picnic table.
Stibal said that without warning, a brief downpour hit about 10:45 p.m.
"It came down in buckets," he said. "I've never seen it rain that hard."
Mud began flowing within five minutes and Stibal and his wife drove away down the hill, Stibal said.
When they returned a short time later, the yard was inundated. They called 911 and fire crews arrived to drain water and lay out sandbags.
Stibal said he had spent $35,000 to protect the steep slope behind his house by installing chain-link fencing and a concrete drain known as a swale, but the mud came down a slope above an adjacent home.
Next door, Lien Yang shoveled mud from his driveway.
"It came very fast," he said.
Yang said he and his wife had been watching TV news before the cloudburst but saw no warnings about an approaching storm.
Residents of about a dozen homes left overnight, Martin said.
"Soon as they heard the rumblings of the mountains coming down, they all got in their cars and got down in safe areas," Martin said.
The neighborhood about 10 miles north of Los Angeles sits below slopes blackened by the 250-square-mile Station Fire and had been designated as being at high risk of mudslides. The blaze, which started in August, resulted in the deaths of two firefighters who drove off the road in thick smoke.
The debris flow apparently was set in motion by a brief downpour.
"This was an uncharted storm, and we had 1 to 2 inches of rain in less than 20 minutes," county fire Inspector Frederic Stowers said.
The mess was a warning that the area remains vulnerable when winter storms come, Martin said.
"Our lesson from this is: it's just what we had feared," Martin said. "When the rains start to come, we need to evacuate."