Southern Pacific classes GS-1 and GS-2

In 1930, the Southern Pacific used its Mountains as a base and installed a larger firebox, now supported by a two-axle bogie. This resulted in the GS-1, which was intended for passenger and express trains with a driver diameter of 73.5 inches or 1,867 mm and was built by Baldwin. GS stood for “Golden State” or later “General Service”. Ten GS-1 were delivered directly to the Southern Pacific and four to the Texas & Louisiana Lines.

In 1937 six GS-2s were delivered from Lima. They were almost identical to the GS-1, but had colorful streamlined fairing, making them about 6,000 pounds heavier. The famous GS-3 to GS-5, which had larger drivers, were later built with the same fairing. Since the GS-1 and -2 soon no longer had to pull the fastest trains, they were considered for heavy commuter trains. Especially in the San Francisco area, they had to prove their power in demanding schedules until the second half of the 1950s.