Baldwin Locomotive Works erected the first fourteen 4-8-4s for the Southern Pacific Lines in 1930, reportedly using the railroad's own design modified from a 4-8-2. These GS-1 class engines rolled on 73-inch drivers (one source gives 73½ inches), with cylinder dimensions of 27x30 inches. These oil-burners had a boiler pressure of 250 p.s.i., exerted 62,200 pounds of tractive force, and weighed around 445,000 pounds (the sources give different figures). They had a grate area of 90.4 square feet, with 4860 square feet of evaporative heating surface and a proportionately high 2655 square feet of superheating surface.
The first group of GS-1s were assigned to SP subsidiary Texas & New Orleans with road numbers 700-703, and to the SP's "Pacific Lines" as Nos. 4400-4409. In the early 1940s seven "Pacific Lines" GS-1s were transferred to the T&NO as Nos. 704-710. The above photo of unknown provenance, contributed by Gary Thompson, shows the last engine of this group, the original SP number of which is uncertain. Eventually there were eight GS classes, after the 4-8-4s of SP subsidiary St. Louis Southwestern (the "Cotton Belt") were absorbed into the SP numbering scheme late in the steam era. The classification "GS" stood for "Golden State," alternatively for "General Service."