UP 3985 was one of the second versions of the Challenger. She was built in July, 1943 by ALCO and her design drew heavily on experience with the famous Big Boy locomotives. She has 69 inch drivers, boiler pressure of 280 lbs per square inch, and four 21 x 32 inch cylinders. Locomotive and tender weigh about 1,073,900 pounds and can produce 97,350 pounds of tractive effort. UP 3985 last operated in regular service in 1957. After years of storage in the roundhouse at Cheyenne, UP 3985 was placed on an outdoor display beside the Cheyenne depot in 1975 and remained there until she was rebuilt for excursion service in 1981. UP 3985 approaches the photo line on the Wyoming mainline.