So far, the fire is 30 percent contained.
The Yolo County Sheriff ordered additional mandatory evacuations on Thursday morning.
Firefighters have been using aircraft, bulldozers and backfires to curb the blaze.
No homes have burned but some areas have been under evacuation orders for days.
The fire department said the blaze is showing "extreme fire behavior" as it burns through tall grass, brush, and dense oak. "But it's still hampering our efforts and it's an area of concern", he said.
The fire began Saturday afternoon, and by dusk, it had spread to a few thousand acres in and around Guinda, a rural community about 72 kilometres northwest of Sacramento. That's a bit below last year's acreage to date - which included the beginning of California's devastating fire season - but above the 10-year average of 3,600 square miles.
Around the same time, mandatory evacuation orders were expanded to include the area west of Highway 16 to Berryessa Knoxville Road from Old County Road 40 to County Road 53 in Yolo and Napa counties. But Cal Fire says crews gained some ground and got more control over the flames.
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