| During the last shoppings at Cheyenne in 1957, UP 4017 sits disassembled with a cylinder boring machine attached. On the next track, UP 4021 is shown. 4017 was built in December of 1941, the 4021 was built in 1944. 4021 was scrapped in 1962, while 4017 was donated for display to the National Railroad Museum in Green Bay, Wisconsin. Obtained from Union Pacific Steam: Big Boy Portraits (Bush, Ehernberger) |