UP has its own police with full law enforcement powers. I would be curious to know if that force has been downsized. They did abandon the police headquarters building at the western edge of the LA yard.
They can arrest but they cannot prosecute. The state needs to try the suspects and enforce any penalties. UP police cannot do the latter -they can only arrest.
Maybe they can seek trial in a different locale if the railroad right of way has different jurisdiction.
The only other option the UP police have is asking a federal prosecutor to take the case. And that's only if there's some credible evidence of a federal law violation.
I'm not generally one for expanding federal jurisdictional reach, but there's a much clearer federal connection for: internationally imported shipping containers leaving a federal port facility on a (primarily) federally regulated mode of transportation devoted (primarily) to interstate commerce... than there is for 90% of what legally gets classified today as federal jurisdiction.
Maybe they can seek trial in a different locale if the railroad right of way has different jurisdiction.