Cal Fire firefighters Monday returned to a rugged area of Sonoma Coast State Park to make sure Sunday's timber fire there remained extinguished.

One Occidental firefighter suffered heat exhaustion during Sunday's effort.

The firefighter was taken by ambulance to Palm Drive Hospital for treatment, said Occidental Fire Chief Ron Lunardi.

The fire burned about two acres of timber near Willow Creek.

The cause remained under investigation Monday, but fire officials said it could have been from an illegal campfire.

Cal Fire, Occidental, Monte Rio, Graton and Gold Ridge firefighters worked on the effort.

Firefighters first had to hunt for the remote fire after callers reported smoke at about 7:40 a.m. The park is accessible by road from Coleman Valley Road, west of Occidental, or from Highway 1 near Jenner.

Firetruck engineers drove in as far as they could and then a Cal Fire bulldozer operator cut a new path to allow engines and water trucks to get closer.

Crews were at the fire until Sunday night and then returned early Monday.