The last and heaviest Mikados built for the Frisco were the 20 locomotives numbered 4200 to 4219. Like most of their predecessors, they had drivers of 63 inches and cylinders of 27 by 32 inches. At a boiler pressure of 235 psi, they delivered a starting tractive effort of 73,965 pounds and a trailing truck booster added another 9,600 pounds. They had a mechanical stoker, a coffin feed water heater, two thermic syphons and arch tubes. They were retired between 1953 and 1956.

The Frisco Lines received a total of 65 Mikados with additional booster between 1923 and 1926, based on the USRA Heavy Mikado. The first 35 locomotives had Baker valve gear and were fired with coal or oil, depending on the lines. The locomotives from number 4135 had Walschaerts valve gear and thermic syphons. Starting with the 4150, the heating surface has been increased. The first 35 locomotives were later also given Walschaerts valve gear and thermic syphons, as well as slightly larger driving wheels. They were dismissed from service in 1951 and 1952.