Residents from two streets in Riverside County were advised to evacuate Thursday night at the peak of the fire that burned about 150 acres in and around Rancho Jurupa Regional Park, county Fire spokeswoman Jody Hageman said.
It was not clear how many people left their homes, but no one had sought refuge at a shelter established for evacuees.
About 200 firefighters helped by helicopters took on the blaze whose bright flames and huge plumes of smoke were visible from long distances.
The fire was 20 percent contained around midnight, hours after it began. The threat to homes was mostly beaten back, but firefighters were expected to work well into Friday to contain it.
There were no reports of any injuries or homes or buildings burning, but the blaze brought down power lines and left more than 1,800 customers without power, fire officials said.
Video from television news helicopters showed a backyard trailer go up in flames about a quarter-mile from the fire lines in a neighborhood where embers were flying, but fire officials couldn't immediately say whether the wildfire embers sparked it.
"You never know how far they'll go," county fire Capt. Lucas Spellman told KCAL-TV. "Normally they don't go that far, but I can't say for sure."
To the west in Los Angeles, a fire sparked the underbrush near homes at the top of the Cahuenga Pass but firefighters and water-dropping helicopters made quick work of it.
The fire broke out at 2:39 p.m. Thursday just east of Interstate 101 and California Route 170, and was knocked down in less than an hour, city fire spokeswoman Katherine Main says.
The fire burned about one acre and no structures were damaged, although flames came very close to some homes and traffic on the nearby freeways was slowed, Main said.
The National Weather Service issued an advisory for gusty offshore winds for valleys in Riverside County and elsewhere in Southern California that will be in effect until Saturday afternoon.
About 200 miles north of Los Angeles in Inyo County, a wildfire that consumed more than 400 acres in the high desert Lone Pine area was fully contained after burning for four days.