REDDING, Calif. (AP) — Union Pacific Railroad crews are working to put two box cars back on the tracks following a derailment in far Northern California. Union Pacific spokeswoman Calli Hite says four of 67 cars on a freight train heading from Roseville, Calif., to Portland, Ore., derailed around 4 p.m. Monday near Redding. No one was hurt, but Amtrak service on the line was affected. Hite said the cause of the derailment is under investigation. Three of the cars were empty, while the fourth had scrap paper. The paper did not fall out. Two of the cars have since been righted and put back on the tracks. Amtrak spokeswoman Vernae Graham said Amtrak was bussing passengers between Sacramento, Calif., and Klamath Falls, Ore.