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 had not been determined Friday afternoon.
It was very slow, methodical work, but after nearly 12 hours Union Pacific work crews were finally able to untangle the wrecked rail cars and pull the two mangled trains apart.
All in all, things could have been much worse.
The trains collided just before midnight at an unknown rate of speed.
A conductor and engineer on the westbound train were hospitalized.
The conductor lost his arm in the crash, but his injuries aren't life-threatening.
"Our hearts go out to the families of the train crew affected with this incident, and we're very happy that we didn't have any fatalities," said Union Pacific Spokesman Aaron Hunt.
What exactly happened Thursday night? Friday's confirmed details were that a westbound freight train crashed into another freight train, one that was backing up in an eastbound direction on the same track.
It may have been human error or it could have been technical failure.
"The first thing we start to look at is all of our signals and all of our dispatching records, so we freeze all of that and we start to assess those, and we also go in and we download the information from the computers on the locomotives and start to look at what was happening inside the locomotive," said Hunt.
As crews work to try to reopen the tracks, they're thankful. While this was a destructive train crash, at least it wasn't a fatal train crash.
"Fortunately we had no fatalities in this incident last night and our crew, they're in stable condition, and we're very fortunate from that perspective," said Hunt.
Freight service and Amtrak utilize the affected train tracks, but they were able to use other tracks and were not otherwise affected. Metrolink does not use the tracks.
Union Pacific was expected to have the tracks back to normal by 10 p.m. Friday.
Do you want the Eyewitness News team to call you? Get a FREE Morning Wake-up Call and personalized weather report at abc7.com/wakeup