In Altadena, mud flowed down a road during a flash flood in front of a bulldozer clearing debris in the Eaton Fire zone, while in the Pacific Palisades images showed a police officer stood at a junction in ankle-high flood waters.
In Altadena, where a road in the north was also submerged by three feet of mud, vegetation and trees, Mehran Daoudian prepared by laying a sheet over a hole in his home's roof where fire had burned through it last month.
In Pacific Palisades, one of the affected areas in last month's wildfires, one intersection of the highway was submerged in at least three feet of sludge.
Southern California could get as much as six inches (about 15cm) of rain in the mountains and three inches (nearly 8cm) in coastal areas and valleys before the system moves out on Friday, said Brent Bower, a weather service hydrologist.
A swift flow of debris saw a Los Angeles Fire Department vehicle being swept off the Pacific Coast Highway and into the ocean in Malibu on Thursday.
