Authorities responded to the park, located at 500 Ragle Road, at about 5 p.m. Friday, and found the man's body, according to the coroner's office.
The man had no identification with him and was believed to be jogging.
He is described as white, 5 feet 10 inches tall and is believed to be 45 to 55 years old. He has an athletic build with blond and gray hair, blue eyes and a goatee.
The man was wearing blue Hind running shorts; an orange, gray and black First Ascent tank top; and black Vibram shoes that are a European size 42. He had a rainbow beaded bracelet on his right wrist.
Authorities believe the man died of natural causes, and the case is being investigated by the coroner's office.
Anyone who may know the man's identity is asked to call the Sonoma County coroner's office at (707) 565-5070 or (707) 565-2121.