Costa Mesa police Lt. Mark Manley says the car was stopped on Irvine Boulevard shortly before 2 p.m. Thursday when the tree, estimated between 40 and 50 feet tall, toppled over from the center median and onto the vehicle.
Manley says the female driver of the blue Hyundai sedan was pinned inside the car. He says she initially was alive and responsive but died while paramedics were trying to free her.
Manley says the woman was the only person in the car. She hasn't yet been identified.
Manley says authorities do not yet know what caused the tree to fall.