The situation may get worse, with temperatures pushing into the high 90s this weekend, an abundance of dry grass because of an ongoing drought and offshore northerly "sundowner winds" that could spread the fire.
The blaze already is having an effect on tourism, with several state beaches and campgrounds shut down.
So far, nobody has been killed or badly injured, Santa Barbara County Sheriff Bill Brown said at a news conference. About 400 mandatory evacuation calls have been placed, he said, though it was difficult to know exactly how many people actually left because of the rough terrain and scattered housing in the area.
Called the Sherpa Fire, the blaze started Wednesday and burned about 250 acres the first day, CalFire said. The cause of the fire has not been determined.
As of Friday morning it had consumed about 4,000 acres and was 5% contained, said Susan Klein-Rothschild with the Joint Information Center in Santa Barbara.
Flames spread quickly through the hilly land and twice forced the closure of the 101 Freeway, though the road reopened Friday morning, officials said.
Mandatory evacuation orders were issued for El Capitan Canyon, El Capitan Ranch, El Capitan State Beach, Refugio State Beach, Refugio Canyon, Venadito Canyon, Las Flores Canyon and areas east of the Refugio burn area out to Calle Lippizana near an equestrian center, according to the County of Santa Barbara web page.
Santa Barbara County Fire Chief Eric Peterson said about 1,200 firefighters are working to contain the fire. Thirty aircraft and 61 fire engines were involved, CNN affiliate KYET reported.
Ron Laskin, who lives about 10 miles from the fire, said people can see the blaze far away.
"It is strange seeing something like that while life goes on relatively normally for everyone in town." he said.
Brown, the sheriff, urged people to take the evacuation orders seriously and think about what objects they'd want to take in case of an evacuation.
"We do not want our residents to have a false sense of security," he said. "Don't wait until the last minute to be prepared."
In Arizona, a blaze called the Cedar Fire has burned about 9,600 acres
in the eastern section of the state but growth appears to have slowed because of good work by firefighters and lighter-than-expected winds, fire officials said Friday at a news conference.
Navajo County Sheriff K.C. Clark said he thought the area was "out of the woods."
About 600 people are fighting the fire that started Wednesday on the White Mountain Apache Tribe reservation. Pre-evacuation orders have been issued for of Show Low and Pinetop.