The St. Louis-San Francisco Railway bought thirty Mountain (4-8-2) type locomotives from Baldwin for freight and passenger service. #1501 is from the first batch of fifteen (#1500-#1514) delivered in 1923. Five more (#1515-#1519) were delivered in 1925 and the last ten (#1520-#1529) in 1926.
Oil burning #1500-#1514 were equipped with Baker valve gear, but initial problems led the Frisco to order the rest of the T-54s with Walschaert valve gear. At 339,800 lbs, the first batch
were also lighter than those delivered in 1925 (342,200 lbs) and in 1926
(360,890 lbs). However, all thirty of the class operated at a boiler pressure of 210 psi delivering tractive effort of 56,800 lbs.