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.