The blaze was spotted from the fire lookout station on Mount Barnabe at about 2:30 p.m., Marin County fire Capt. Mike Giannini said.
Firefighters were able to pinpoint the location of the fire, which was burning near the 1000 block of Hicks Valley Road.
Marin County fire and Cal Fire crews responded and controlled the blaze by about 4 p.m. using ground equipment, air tankers and helicopters, Giannini said.
No structures burned and no injuries were reported.
Crews will remain at the site of the fire overnight to ensure there are no flare-ups.