One of the largest locomotives ever operated during the excursion era was Union Pacific 3985, which featured the 4-6+6-4 "Challenger" wheel arrangement. Massive but graceful, the UP Challengers were extremely capable dual-service locomotives capable of running 70 mph with a passenger train or hauling a heavy freight.
I only saw the 3985 in operation once during her career. Here she is seen at the Salt Lake City depot, awaiting an excursion the next day to Provo, UT. The late afternoon sun illuminates every detail of her 122 feet.
Future TPOTDUnion Pacific