A torrent of early morning showers spurred an evacuation order in Orange County, where at least 1,500 people in Yorba Linda were told to leave their homes.
"Nothing has gone down yet, but the rain met the threshold where we needed to get people out," Orange County Fire Captain Greg McKeown said.
Voluntary evacuations had already been called for in the city of 65,000 southeast of Los Angeles, which was torched by a huge fire earlier this month.
In another wildfire-ravaged area in Santa Barbara County, an evacuation order affecting up to 2,200 homes remained in effect Wednesday morning after light rain had fallen in the area for several hours.
"The fire wiped out all vegetation and the soil is very unstable," said county spokesman William Boyer. "We're talking about some very steep slopes up there."
Flash flood warnings were issued Wednesday morning in wildfire-charred areas in Ventura, Los Angeles, Riverside, San Bernardino and Orange counties.
In northern Los Angeles County rain was falling at nearly an inch per hour.
Homeowners hurriedly stacked sandbags on Tuesday and Gov. Arnold Schwarzenegger ordered state agencies to prepare to aid local agencies in case of disaster.
"The state stands ready to help local governments protect lives and property," he said.
A low-pressure area off the coast was heading northeast and could bring an inch of rain through Thanksgiving and up to 4 inches in the mountains, said Stan Wasowski, a forecaster with the National Weather Service in San Diego.
A series of wildfires stoked by Santa Ana winds damaged or destroyed about 1,000 homes in Los Angeles, Orange, Riverside, Santa Barbara and San Bernardino counties this month. Those burn areas combined equaled about 65 square miles. In addition, October wildfires burned dozens more homes and scorched the equivalent of more than 35 square miles. Other areas remain scarred from fires in recent years.
More than 135 members of the California Conservation Corps were sent to canyons in Yorba Linda to place sandbags and clean out culverts and spillways to handle runoff.
Heavy equipment operators placed lines of portable concrete barriers below the denuded hillsides of Chino Hills State Park to redirect potential storm flows away from Yorba Linda homes. Ninety percent of the wilderness park burned.
Without the fire-related risks, rain might be appreciated in parched Southern California. Downtown Los Angeles had recorded only .27 inch of precipitation since the July 1 start of the rain year -- 1.35 inches below normal for this time.
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