DAVENPORT, Calif. — Thick, white smoke filled the air around Santa Cruz Saturday as firefighters battled a Northern California wildfire in steep, rugged terrain.

The Lockheed Fire in the Santa Cruz Mountains has blackened close to 21 square kilometres of remote wilderness since Wednesday and prompted mandatory evacuations of the mountain communities of Swanton and Bonny Doon, which have about 2,400 residents and several wineries.

The fire didn't spread overnight, and was 30 per cent contained Saturday morning, said CalFire spokesman John Buchanan. No homes had been destroyed, and no injuries were reported. The blaze damaged two small structures and was threatening more than 1,000 homes and buildings. The cause is under investigation.

Other blazes throughout the parched state have forced evacuations and knocked out power. Smoke from a blaze in Yuba County north of Sacramento could be seen as far away as Reno, Nevada.

Lt. Gov. John Garamendi declared a state of emergency Friday for Santa Cruz County. Gov. Arnold Schwarzenegger, who has returned to California after attending the Massachusetts funeral of his mother-in-law, Eunice Shriver, was scheduled to visit the fire zone Saturday.

The Lockheed Fire started Wednesday about 16 kilometres north of Santa Cruz. A change in winds shifted the fire away from Bonny Doon but closer to Swanton, CalFire spokesperson Daniel Berlant said.

The steep, rugged terrain and dense vegetation have made it difficult to contain the blaze, so firefighters have focused on keeping flames away from homes, said Jim Stunkel, a battalion chief from San Jose.

"As the brush ignites, it's like a fireworks explosion, and the sparks rain down where the ranch houses are," he said.

Chris Sokoloff, 40, an electrician who moved to Bonny Doon from Portland, Oregon, a week ago, spent the night at an evacuation centre in Santa Cruz.

"It's really hit home this morning, seeing all the ash on the vehicles," Sokoloff said. "I got a big red hockey bag and that's all I got right now."

Meanwhile, about 250 homes and ranches in canyons and ridges near a wildfire in the Los Padres National Forest remained under evacuation orders. The week-old fire has grown to nearly 306 square kilometres, said U.S. Forest Service spokesperson Vicki Collins.

In Yuba County north of Sacramento, a wildfire covering more than 400 kilometres Friday destroyed two homes, forced the evacuation of about 120 residences and knocked out power in the Sierra foothills town of Dobbins, according to CalFire spokesperson Joann Cartoscelli.

In Alameda County, more than 300 firefighters were struggling to control a wind-driven grass fire that had grown to about 60 square kilometres near Tracy, according to a CalFire report. The Corral Fire was about 20 per cent contained.

More than 400 firefighters had contained about 35 per cent of the fire -- about double what was contained the night before -- and were expected to make a decision Saturday afternoon on whether some residents could return to their homes, Cartoscelli said.

In far northern California, Trinity County District Attorney Michael Harper has charged 60-year-old Brenda Eitzen of Los Molinos with two felonies and two misdemeanours alleging she negligently sparked a blaze by throwing away a lit cigarette Wednesday. The charges could bring a maximum four-year prison term. The Coffin Fire was expected to be contained later Saturday.