Updated

Firefighters on Monday made progress against a handful of wildfires across Southern California amid triple-digit temperatures and the threat of thunderstorms.

From Los Angeles to San Bernardino counties, hundreds of firefighters struggled to contain blazes that scorched hundreds of acres of dry brush, but no homes were threatened and there were no reports of any injuries.

Thunderstorms were expected again Monday that could bring lightning strikes which is responsible for at least one of the fires.

In Angeles National Forest, a blaze burned about 350 acres six miles south of Acton and was 20 percent contained, authorities said. Nearly 400 firefighters and several water-dropping aircraft were at the scene. Full containment was expected by Tuesday.

The cause of the blaze is under investigation.

Another fire had charred about 200 acres near Elizabeth Lake in the Lancaster area and was 50 percent contained. More than 80 firefighters were helped by cooler, overnight temperatures that allowed them to get better control over the fire, said Inspector Jason Hurd of the Los Angeles County Fire Department.

"The fire laid down pretty good last night and there is no visible smoke right now," Hurd said. "But there is a good probability of spotting outside the (containment) line and a spark could cause a problem."

Lightning was believed to have started the blaze, Hurd said. Someone saw the lightning bolt that ignited the blaze, he said.

Meanwhile, firefighters tackled an 85-acre wildfire in the San Bernardino National Forest at the east end of Big Bear Lake. The blaze was 45 percent contained, but it forced the closure of a five-mile stretch of Highway 18, fire officials said. The road was expected to reopen Tuesday. The cause of the fire also is under investigation.