Union Pacific SD40-2 3227, UP SD40-2 3284, UP SD40-2 3162, UP C30-7 2437, D&RGW GP40-2 3099 and Mountain Diesel FP7 1510. No photographer listed on slide.
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.