A rogue wave caused the private fishing boat to capsize in the cold waters of Bodega Bay on the first day of crabbing season. The dead included three men and one woman.
US Coast Guard troops "pulled four unresponsive people from the water. One was pronounced dead," the Sonoma County Sheriff's Office said.
Three others were carried to shore and taken to hospital via ambulance, where they were administered cardiopulmonary resuscitation.
"Regretfully, none of the four survived," the statement said.
A sheriff's department helicopter, however, was able to remove an adult man, identified as 66-year-old Phillip Sanchez, from Bodega Rock.
"None of the people aboard were wearing life vests, although they were present and available on the boat."
The sheriff's office said alcohol or drug use were not believed to be at fault in the tragedy.