The Southern Pacific GS-4s were designed for high-speed passenger service and were used on Southern Pacific's premier passenger trains, the Coast Daylight, San Joaquin Daylight and Sunset Limited, as well as many other Southern Pacific name trains. In later years they were painted black and had their side skirting removed for easier maintenance, and were re-assigned to the San Jose-San Francisco commute trains, freight service, and the occasional San Joaquin Daylight until new diesels arrived and they were retired.