Flames from the 31,000-acre Chimney Fire at Lake Nacimiento spread from San Luis Obispo County into Monterey County, Cal Fire reported Monday.
Firefighters said their top priority this week is halting the wildfire from spreading further north in Monterey County.
The Chimney Fire is about five miles from Lake San Antonio on its north end, and three miles from Hearst Castle on its south end.
The Chimney Fire broke out August 13 in the area of Gage Irving Road near Lake Nacimiento and destroyed 34 homes. Its cause remains under investigation, and 1,800 structures are still threatened.
Containment of the Chimney Fire remained at 35 percent Monday afternoon.
Further north toward Big Sur, the Soberanes Fire has charred 86,294 acres.
The Soberanes Fire is spreading mostly southeast into Los Padres National Forest, and is 60 percent contained. Cal Fire said full containment is expected by September 30