The fire in Pope Valley grew to nearly 6 square miles Wednesday, a day after it broke out, said Daniel Berlant, a spokesman for the California Department of Forestry and Fire Protection.
It damaged nine structures including two homes and threatened hundreds more, officials said. But it was burning to the north of the county's famous vineyards.
"It has not come anywhere close to what we consider Napa Valley wineries," said Cate Conniff, a spokeswoman for the Napa Valley Vintners, a nonprofit trade association. "It is moving in the opposite direction, and it continues to move that way. We're keeping an eye out on it." Pope Valley is about 20 miles north of Napa Valley.
More than 1,000 firefighters were hoping to get a better handle on the blaze after they made progress overnight Tuesday, Berlant said. But fire activity increased about noon Wednesday as temperatures again soared into the 90s and the blaze continued burning northeast into neighboring Lake County. The fire is 30 percent contained, officials said.
Crews have requested more bulldozers from across the state to assist the dozen on site in strengthening containment lines, Berlant said.
No injuries have been reported, and the cause of the fire remains unknown.
The fast-moving blaze began Tuesday afternoon in Napa County. Within hours, it covered 600 acres and then spiked to 2,700 acres by late evening as it spread northeast. State firefighters and crews from Napa, Lake and Solano counties spent a second day working in 90-degree weather on Wednesday.
Similar high temperatures were expected again on Thursday. The fire exploded because of dry conditions across the state, Berlant said.
Gov. Jerry Brown said Wednesday that he has secured federal funds to help fire departments absorb some of the cost of fighting the fire.
Elsewhere in California, firefighters were surrounding a blaze in Shasta-Trinity National Forest that forced the evacuation of about 15 homes. Forest spokeswoman Andrea Capps said the fire has burned through 35 acres since it started Tuesday and was 70 percent contained.