Searchers on Monday spent a third day looking for a Sacramento man missing in Annadel State Park.
About 40 searchers took to the park's trails and rugged hillsides, hoping to find the 34-year-old man, Sonoma County Sheriff's Lt. Bret Sackett said.
The man disappeared Saturday morning after parking on the eastern edge of the huge park.
Sheriff's officials have declined to identify the man, saying he has mental health issues.
The man on Saturday morning drove along rural Lawndale Road in the Sonoma Valley and parked on private property. A neighbor who spoke to him as he headed into the park told deputies that the man wasn't making sense.
Searchers believe the man was last seen Saturday evening by a teen on a mountain bike.
The teen said the man was naked and chanting, Sackett said.
Searchers headed for that area and found no sign of the man or his clothing and hoped he had gotten dressed to better protect himself during the night's cold.
By Sunday, the search included well more than 100 people from at least four counties, including dozens of trained search and rescue volunteers.
Word of the search also spread among park visitors Sunday.