An infusion of fresh manpower helped firefighters gain the upper hand Tuesday on a wildfire (search) that had burned across more than 12,500 acres and destroyed four homes in Northern California's wine country.

Cooler, moist air that had been forecast for the region failed to materialize during the night, but the extra personnel more than compensated for the poor weather, said Janet Marshall, spokeswoman for the state Department of Forestry and Fire Protection.

With more than 2,600 firefighters on the front lines, up from 1,110 a day earlier, officials said the blaze in Sonoma and Lake counties was 85 percent contained Tuesday morning, up from just 35 percent the night before.

"There is a saying that many hands make light work, and while this certainly isn't light work, the extra help has allowed us to make great strides and progress," Marshall said.

Full containment of the fire, in uneven and often steep terrain, was not expected until Wednesday, she said.

The blaze started Friday about 60 miles north of San Francisco and has fed on tinder-dry brush, with flames driven by dry, unpredictable wind. Authorities initially were concerned that the fire would threaten the vineyard area of Sonoma's Alexander Valley, but the fire shifted directions from south to east. The vineyards aren't considered threatened now, Marshall said.

In addition to the four vacation homes, the fire had destroyed eight outbuildings and an electrical equipment storage vault owned by a local utility, Marshall said. About 40 residents had been evacuated.

Seven firefighters were injured.

State officials gave Calpine Corp. and Pacific Gas & Electric Co. permission Tuesday to fire up major power lines through the area that had been shut down to prevent injuries to firefighters, Marshall said.