The fire, which started Friday northeast of Geyserville in Sonoma County, had been 20 percent contained and full containment was not expected until Wednesday, said Janet Marshall, spokeswoman for the state Department of Forestry and Fire Protection.
The unpredictable wind and dry vegetation, compounded by uneven and often steep terrain, made the situation extremely dangerous for the 1,875 firefighters, Marshall said.
"These are very erratic winds, which can be blowing perpendicular to one another," she said. "You never know where they're coming from, and that's a huge safety concern for firefighters."
Two firefighters had been injured, but not critically.
In addition to the four homes, eight outbuildings and 12 cars had been destroyed. About 40 residents had been evacuated from the area, about 60 miles north of San Francisco, including occupants of six homes ordered evacuated Monday morning, Marshall said.
Others living in the area were urged to have evacuation plans ready because the blaze was considered to be threatening 200 other houses and five businesses.
The fire also threatened major power lines from 21 generating plants in the Geysers, the world's largest geothermal power facility.
On Saturday, two-thirds of the plants and two transmission lines were shut down, said Kent Robertson, a spokesman for Calpine Corp., which owns the lines. The company rerouted electricity from other plants and no outages were reported.
According to the U.S. National Interagency Fire Center, 2004 has been one of the worst years for wildfires in recent memory. With more than 7 million acres burned to date, 2004 is on track to be the worst fire season since at least 1988.