It is now 60 percent contained as of midday Tuesday.
Firefighters received a report of the fire at 10:47 a.m. near Mix Canyon Road and Sky Ranch Lane, a Cal Fire dispatcher said.
[Ads /]
The fire is threatening ten to 12 nearby homes and voluntary evacuations are in effect, according to fire officials.
Mix Canyon Road remains closed.
The fire appears to have started when a vehicle caught fire and investigators are now looking into what caused the vehicle fire, Cal Fire said.
Firefighters from Vacaville, Dixon, Fairfield, Suisun City and Cal Fire are all assisting to put out the fire, according to fire officials.