About 100 homes remained evacuated.
The fire spewed a plume of smoke visible for miles. It was burning in steep, rugged terrain near Clayton, a town of about 11,000 people northeast of San Francisco, alongside the park.
Some 800 firefighters, aided by two air tankers and three water-dropping helicopters, were battling the blaze. Three of them suffered minor injuries.
The Bay Area Air Quality Management District issued a smoke advisory Monday for parts of Contra Costa, Alameda and Santa Clara counties. Residents were advised to take precautions, including setting air conditioning units and car vent systems to recirculate.
Elderly people, children and those with respiratory illnesses were told to be particularly careful.