A brush fire grew to cover 20 acres after breaking out near Mount Baldy Friday evening, authorities said.
San Bernardino County, Los Angeles County and Angeles National Forest firefighters responded to the wildfire, which was first reported shortly before 8 p.m. at Shinn and Mt. Baldy roads, the San Bernardino County Fire Department announced via social media.
It was being dubbed the San Fire.
The fast-spreading blaze grew to 10 acres by 8:15 p.m., Los Angeles County Fire Department Dispatch Supervisor Ed Pickett said. The fire was working its way uphill, officials added.
It had scorched about 20 acres by 9 p.m., officials said. But at that point, its rate of speed had slowed.
The flames were 0 percent contained, and fire crews would remain on scene to continue battling them overnight.
No structures were immediately threatened, officials added.