Five farmworkers were killed and another sustained major injuries as the van in which they were riding was hit broadside by a pickup truck on Highway 4 at Van Allen Road east of Stockton.
The impact sent the van tumbling. It came to rest on its roof. None of the dead was wearing a seatbelt.
CHP Officer James Smith says the fog was so thick that visibility had dropped to less than 200 feet.
"If there hadn't been fog possibly the vehicle would have seen each other sooner and slowed down, at the very least, reduced the force of the impact, reduced their speed so less force in the impact," says Smith.
Smith says the driver and passenger in the pickup suffered only minor injuries. The CHP's Major Accident Injury Team is investigating.