The Southern Pacific built a fleet of 4-8-2 Mountain type locomotives in the late 1920s in its Sacramento Shops. In 1930, the SP designed a locomotive similar to those Mountains that had a very large firebox (90.4 sq ft) and a four wheel trailing truck to support it. Thus, evolved the Southern Pacific 4-8-4 which was designated Class GS (Golden State) by the SP.

The first 10 "Golden States", Class GS-1 (road numbers 4400 through 4409), were built by the Baldwin Locomotive Works in 1930. They were oil burners with 73.5" drivers, 27 x 30 cylinders, and 250 psi boiler pressure, which resulted in a tractive effort of 62,200 lbs. They weighed 448,400 lbs and had 266,500 lbs of weight on the drivers.

In early 1937, six more "Golden States" arrived but this time from the Lima Locomotive Works. These were designated Class GS-2 and assigned road numbers 4410 through 4415 and were identical to the Class GS-1s except for the exterior styling, color scheme plus they weighed 6000 lbs more. The color scheme used bright orange, red, black and silver. The orange was applied to the pilot and in a broad band along the skirting and the tender. The red was applied in a band above the skirting and above and below the orange band on the tender. The rest of the locomotive was black except for the smoke box door, which was silver, and the hand rails, which were cadmium plated. The six Class GS-2s were purchased for brand new trains that updated passenger service between Los Angeles and San Francisco. They sported a "Daylight" emblem and regularly hauled "The Coast Daylight".

Late in 1937, 14 more "Golden States" (road numbers 4416 through 4429) were delivered from Lima. This group, Class GS-3 was similar in appearance to the GS-2s. However, they were designed for higher speeds with 80" drivers, 26 x 32 cylinders, and a boiler pressure of 280 psi giving them 62,800 lbs of tractive effort. They weighed 460,000 lbs and had 267,300 lbs over the drivers.

The Southern Pacific ordered 28 more Class GS-4 "Golden States" from Lima and took delivery of twenty (road numbers 4430 through 4449) in April and May of 1941 and the other eight (road numbers 4450 through 4457) in March and May of 1942. These were similar to the GS-3s except they had "all-weather" vestibule cabs and had a smaller cylinder diameter (25.5) with a higher boiler pressure (300 psi). They weighed 475,000 lbs and with 275,700 lbs on the drivers had a tractive effort of 64,800 pounds.

Two additional "Golden States" (road numbers 4458 and 4459), designated Class GS-5, were delivered from Lima in June of 1942 and were similar to the GS-4 except they had roller bearings on all axles and weighed 8,200 pounds more.

During World War II, the SP like most railroads were in need of more motive power and it wanted more GS Class 4-8-4s, but the War Production Board would not permit SP to build more "GS" passenger locomotives. The Southern Pacific redefined "GS" to stand for "General Service" instead of "Golden State" and specified that this group would be used for freight as well as in passenger service. The board then approved the purchase. From then on "GS" officially meant "General Service". Due to wartime shortages, these last 10 Class GS-6 (road numbers 4460 through 4469) Locomotives were built without skirting and were void of the orange and red paint and were delivered from Lima in 1943.

In 1976 4449 was one of three steam locomotives used in the American Freedom Train.

There are two survivors: number 4449, which is operational, at the SP Brooklyn roundhouse in Portland, OR and number 4460 at the Museum of Transportation in St. Louis, MO.