Around 3,000 residents were evacuated in Lake County, about 120 miles north of San Francisco, after huge flames threatened homes and businesses.
California governor Jerry Brown has declared a state of emergency as officials warned the biggest fires were continuing to grow.
There have been no reports of any deaths or injuries.
One wildfire in Lake County had grown to 13 sq miles and destroyed a dozen buildings, California’s department of forestry and fire protection said.
Fire chief Jonathan Cox said more than 230 firefighters using helicopters, bulldozers and other equipment are battling the flames but the rugged terrain has made the operation difficult.
It’s kind of the worst possible combination, Mr Cox said.
Residents have also been evacuated in Tehama County, about 200 miles north of San Francisco, where a wildfire grew to four sq miles.
The blaze destroyed multiple homes and businesses and threatened another 200 buildings, fire chiefs said.
A nearby casino has served as an animal evacuation centre.
Residents also fled a wildfire in Shasta County, about 300 miles north of San Francisco.
The cause of the fires is not yet known but officials said hot weather, high winds and dry conditions were fuelling the flames.
It comes less than a year after California’s costliest fires killed more than 40 people and tore through the state’s wine country in October, causing an estimated $10bn (£7.5bn) in damage.
The rural region was also hit hard in 2015 by a fire that killed four people and destroyed 2,000 buildings.
In December last year, celebrities including Rob Lowe, Paris Hilton and Chrissy Teigen were among thousands of residents forced to flee a ferocious blaze in Montecito, California.
News Source SkyNews