A Mini Cooper driven by Steven Culbertson, 19, of Lakeville, first clipped a car that was stopped for the light at the intersection of Highway 37 and Lakeville Highway and then smashed into the minivan late Saturday night near Novato, about 30 miles north of San Francisco, the California Highway Patrol said.
All occupants of the minivan, Johnathan Maloney, 45, his wife, Susan Maloney, 42, and their young children, Grace and Aiden, died in the impact, said CHP Officer John Sloat. The family was from Sonoma; the children's ages were not immediately available.
Culbertson was being treated at Santa Rosa Memorial Hospital.
The minivan was rendered nearly unrecognizable by the collision.
The Mini Cooper also struck a sedan waiting at the light and three people in that vehicle were hospitalized in Novato with injuries, according to the highway patrol.
"He clipped two vehicles and broadsided the family of four," said Sgt. Trent Cross. "Right now there is no evidence of drugs or alcohol. That could change later, but right now, there is no evidence."
The crash took place near the border of Sonoma and Marin counties, according to Cross.
Two medical helicopters and the Sonoma County coroner were called to the scene. Culbertson was flown by helicopter to the hospital. He was the sole occupant of the car.
Traffic in the area came to a standstill and was backed up for hours.
The Saturday night crash had the highest death toll since the 2007 crash on Highway 101 in Santa Rosa that killed five members of a Windsor family.