Big UP SD50 No. 5078 leads a westbound freight over the crossing with Santa Fe's Stockton Sub at the tower. When freights approached the tower, they would often call the operator for a "light" so they could keep their train moving.
The EMD SD (special duty) series are a strong and reliable kind of locomotive which still serve America's rails today. They have proved themselves reliable by clocking in several million miles of freight service over several decades.