More than 800 firefighters are battling the Marshes Fire just south of Highway 49 near Lake Don Pedro.
The flames are eating through the thick brush as it climbs the hills and that makes it hard for crews to reach points where they can block the fire’s path.
Nancy Longmore with Cal Fire says like most wildfires this one was caused by a careless act.
“A person that was driving a vehicle along Marshes Flat Road pulled over to take a break, parked their vehicle in the dry grass, that vehicle subsequently ignited the grass fire.”
Longmore says 64 engines, 27 bulldozers, and two air-attack planes are on the scene with no prediction for full containment.
She says so far no structures have burned but some are threatened.
"The access to this fire has been particularly difficult. There haven’t been many points where equipment could actually drive to the fire," says Longmore. "We’ve got high tension Hetch Hetchy power lines there that serve the Bay Area and that’s been a concern to keep them out of the fire.”