LOS ANGELES — After a temperate early summer and a balmy Fourth of July, Southern California residents abruptly found themselves in a caldron of triple-digit temperatures and wildfires this weekend.

Firefighters across the region battled several blazes through the night Friday into Saturday, as an unseasonable heat wave set records in some places and knocked out power to tens of thousands of homes in Los Angeles.

In Santa Barbara County, nearly two dozen homes were incinerated in a wildfire that began Saturday, once again harrowing an area ravaged in the last year by fires and then mudslides that killed 21 people.

No deaths were reported on Saturday, but the county said the fire was “causing conditions of extreme peril to the safety of persons and property.” Gov. Jerry Brown declared a state of emergency in Santa Barbara County, mobilizing state resources against the fire.