A large-scale search of Annadel State Park continued Tuesday for a Sacramento man believed to have been in a distressed state when he entered the park last weekend and disappeared.

A combined force of about 80 people, including about 30 searchers organized by the man's family along with search and rescue personnel from multiple agencies, joined the effort for its fourth day, the Sonoma County Sheriff's Office said.

The unidentified 34-year-old was said to be struggling with mental health issues when he parked Saturday morning on private property near the eastern edge of the park, abandoned his car there and walked into the park.

Officials believe a bicyclist saw the man, naked and chanting, on Saturday evening, but no sign of him has been found since, the sheriff's office said.

Search and rescue volunteers from several California counties have joined with Sonoma County Search and Rescue crews since Saturday to scour the landscape for the missing man.

The man was described as standing about 6-foot-6 and weighing 185 pounds. He has sandy brown hair and blue eyes, and was dressed in a T-shirt, blue jeans, orange and black athletic shoes, and a tan jacket when he entered the park.

Anyone with information about his whereabouts is asked to call the sheriff's office at 565-2650.