A discarded cigarette ignited the Golf Fire in Lake County, Cal Fire said Saturday following "a meticulous and thorough investigation."
The fire, which started about 1 p.m. Thursday on Soda Bay Road and Golf Drive in the Lake County community of Kelseyville, has burned about 20 acres and was about 80 percent contained as of Saturday morning.
A spokesman late Saturday afternoon said containment should be higher, but that "they still have a lot of work to do due to the topography and the type of vegetation there."
Crews will thoroughly check the area for spots that could flare up again, he said.
No property damage has been reported in the blaze, but 40 structures were threatened. One firefighter suffered minor injuries in the blaze.
Cal Fire said cigarettes should be discarded in a deep sturdy ashtray away from anything that can burn.
"Do not discard cigarettes in vegetation such as mulch, potted plants or landscaping, peat moss, dried grasses, leaves or other things that could ignite easily," the agency said, advising that dousing cigarette butts and ashes in water or sand is the best extinguishing method.
Cigarettes should never be thrown out of vehicles, Cal Fire said.