COMMERCE, Calif. (June 20) - A line of train cars broke loose in a switching yard and rolled 30 miles toward Los Angeles, picking up speed before derailing and hurling tons of lumber onto trackside homes Friday. The noon wreck demolished two homes and damaged two others, and left a massive tangle of rail cars and lumber in Commerce, a suburb east of Los Angeles. Hours afterward firefighters and dogs continued to search huge piles of debris. News helicopters were asked to back off to allow searchers to use listening equipment in the hunt for any victims. No one was reported missing. Rescue workers examined a dozen people but found only four minor injuries, including a man with arm cuts, two girls who were ``emotionally upset'' and a woman with knee pain, said Van Mark Madrigal, a medical supervisor with the Los Angeles County Fire Department. ``We saw the train demolishing and splintering the house. You saw the power lines going down, the sparks. I was in shock,'' said Jason Mendez, 34. Some witnesses stood outside the debris crying. Others watched in silence as rescue workers combed the wreckage. Luis Carlos Vasquez Jr., 31, was raking in the back yard of one of the homes hit by flying wreckage when he heard the train. ``The sound wasn't right. When I turned around, rocks are flying, there are two box cars in the air.'' He said he rushed inside the house to rescue his sister, who had taken refuge in a closet. ``A pair of wheels fell in front of me. The ceiling was coming down. Debris all over the place. I got my sister and carried her out.'' The National Transportation Safety Board dispatched investigators, spokesman Paul Schlamm said from Washington, D.C. The cars got loose after a freight train stopped in Montclair to switch some cars, Union Pacific Railroad spokesman John Bromley said. The freight cars traveled downhill nearly 30 miles toward Los Angeles before the wreck on a main east-west line. Railroad employees were unable to stop them. ``There was quick consideration whether or not we could derail the cars onto a spur track. Obviously that was not successful,'' Bromley said. The cars eventually derailed on their own in Commerce, a largely industrial community. Authorities estimated that 31 cars ran away and at least 11 derailed. No railroad employees were reported injured, Bromley said.