A vehicle reportedly drove off state Highway 1 and crashed down a seaside cliff near the community of Carmet at about 12:20 p.m., CHP Officer Kevin Bartlett said.
The driver and sole occupant of the vehicle died in the crash, Bartlett said.
Traffic was not affected, Bartlett said.
Officers from the CHP and the Sonoma County Sheriff's Office were conducting an investigation.
It had not been determined if the crash was a suicide, Bartlett said.