This AT&SF 1050 Class Prairie type (2-6-2) locomotive was built by Baldwin in 1902. It was one of one hundred and three delivered to the railroad between 1902 and 1903 as four cylinder Vauclain compounds following delivery of fifty Vauclain compound Prairies in 1901.
The main advantage claimed for compounding was lower fuel and water consumption, but the Vauclain arrangement produced uneven forces and excess wear at the crosshead, which increased maintenance costs and largely offset any fuel economies. The complex valve assembly and the starter valve, which allowed admission of high pressure steam directly to the low pressure cylinder, also increased maintenance costs. By the turn of the century, many US railroads were therefore turning away from compounds and converting those they owned to single-expansion locomotives. The AT&SF subsequently simpled all its 1050s between 1910 and 1922 with 23½" x 28" cylinders.
#1129 served on various AT&SF divisions in New Mexico for fifty-one years, and its last scheduled run ended in Belen, NM, on 25th July 1953.