The 16 Complex fire, which started Tuesday in a remote area of Colusa County, has burned 16,719 acres and was reported 35 percent contained Friday evening.
The complex consists of two fires burning about four miles apart along Highway 16 south of Highway 20.
The California Department of Forestry and Fire Protection reported that an advisory evacuation warning is in effect for the Cortina Rancheria area. Residents are on notice to be prepared for a potential evacuation order.
Fire officials said efforts are being made to protect structures and cultural values in the rancheria and fire area.
They said 23 residences, one commercial structure and seven outbuildings are threatened.
Highway 16 is closed from Highway 20 to the town of Rumsey.
A fire also was reported in neighboring Lake County at 1:10 p.m. Friday and had burned 450 acres by late afternoon.
Officials said the Scotts fire is burning west of Scott Valley Road, on Cow Mountain, eight miles east of Ukiah, and mandatory evacuations are in effect for the Blue Lakes area.