Several people reported seeing the body on the northern edge of the beach beginning around 8:20 p.m., said spokesman Rich Weideman.
The Marin County coroner's office arrived at the beach and confirmed the person found was dead. Weideman said the body was removed between 9:30 and 10 p.m.
"The body was in such bad shape that there's no way to tell the preliminary cause of death," he said.
The coroner's office is working to determine the person's identity and the cause of death.