The Southern Pacific class M-6, originally designated class EF, were Vauclain compound Moguls with drivers of 63 inches introduced in 1901. In the first year, Baldwin built 68 and 23 more were built between 1902 and 1903. Four more identical locomotives went to the Texas & New Orleans. Between 1907 and 1914, all were rebuilt with two simple cylinders and soon also superheated. In 1917 and 1918, the SP built three more in their own shops at Sacramento which were simple and superheated from the start. The class was retired between 1934 and 1958.