Authorities say at least four people were killed and several more suffered serious injuries when a passenger bus overturned on Interstate 10 in Southern California near the Arizona border. Caltrans spokeswoman Terri Kasinga says the crash occurred shortly after 2 a.m. Wednesday just east of Blythe when a big rig jackknifed and spilled a load of steel pipes into lanes. She said the bus either swerved to avoid the pipes or it struck the pipes and overturned onto the shoulder.