The train's engineer was pulled from the wreckage with moderate injuries, but the conductor was trapped.
Batt. Chief Richard Campos of the San Bernardino County Fire Department said the trapped man was in the rail car that was 20 feet off the ground. He had a "heavy amounts of steel on his arm," and a surgical team from a local hospital was called to help extricate that man, Campos said.
The man's arm was amputated to free him from the wreckage.
The railway runs right next to the 10 Freeway, and at one point, the entire freeway was shut down in the area because of concerns that some leaking fluids posed a health threat.
A hazardous materials team responded to the scene. About 500 gallons of fluid, which turned out to be antifreeze, leaked from one of the rail cars. Officials said it was determined that the fluid posed no threat.
The cause of the collision has not yet been determined. Crews are still on scene clearing the accident.
"We're looking at what happened here, why would we have had two trains end up on the same line at the same time," said Aaron Hunt of Union Pacific Railroad.
Officials said they need to analyze signals, dispatching records and other computerized information.
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