The 16 Complex fire two fires about four miles apart in Colusa County was reported 10 percent contained with 3,500 acres burned as of Wednesday night.
The fire is burning in a remote area of Rumsey Canyon, along Highway 16 south of Highway 20.
An evacuation warning was in effect for the Cortina Rancheria area, according to the California Department of Forestry and Fire Protection.
Highway 16 was closed from the junction of Highway 20 to about seven miles east of the Colusa-Yolo County line at Manzanita Avenue.
The cause of the fires, which started Tuesday afternoon, has not been determined. As of Wednesday night, 1,516 fire personnel were on the scene.
Fire activity increased Wednesday in other areas of Northern California as dry lightning sparked more than a dozen wildland fires in the Sierra Nevada and northeastern part of the state, according to Cal Fire.
A low-pressure system spawned a considerable number of thunderstorms that were devoid of rain but still featured lightning, Cal Fire said in a news release.
"With the already tinder-dry conditions, this lightning storm system has elevated the fire danger even higher this week," said Ken Pimlott, Cal Fire director.