Fifty to 60 homes in the Lebec area were actively threatened, although as many as 200 homes had been evacuated, said Michelle Puckett, a spokeswoman for the U.S. Bureau of Land Management.
Firefighters were stationed at each threatened property for structure protection and displaced residents were being sent to a school, she said.
To the west, the community of Frazier Park had not been ordered evacuated by late afternoon, Puckett said.
Residents would be informed by the Kern County Sheriff's Department and the California Highway Patrol if they needed to leave, she said.
About 250 firefighters from Kern County, the BLM and U.S. Forest Service were battling the blaze and many more were en route, authorities said.
The fire was reported at 12:15 p.m. There was no immediate word on the cause.
Huge columns of smoke rose into the sky as flames chewed through stands of pine west of Interstate 5 in the Lebec area of Tejon Pass, about 60 miles northwest of downtown Los Angeles.
Lebec is one of several small communities along I-5 in the pass, which rises to an elevation of more than 4,000 feet between the southern San Joaquin Valley and the Los Angeles metropolitan region.
The National Weather Service said high pressure over the Southwest will keep temperatures hot through Thursday, possibly at record levels in some areas. The high will weaken on Friday and allow some cooling, the NWS said.
Elsewhere in the state, a lightning-sparked blaze burning in Yosemite National Park since Aug. 9 had blackened a total of 160 acres in the Lake Vernon area north of the Hetch Hetchy Reservoir. The National Park Service said crews were managing the fire for ecological benefits.