Quoted By:
The last Class 1 Railroad in the US to retire steam is generally accepted to be the Norfolk and Western, when they retired the last of their big Y6b 2-8-8-2's in June 1960. However, steam survived longer in a few places in mainline, revenue service, such as on the Duluth, Missabe and Iron Range, who ran their M4 Yellowstones, 2-10-4's and 2-10-2's up until 1962, and and ran several excursions in 1963. The Colorado and Southern was still running M-4 class 2-10-2's west of Cheyanne as late as May 1960, and the C&S' Leadville Branch used 2-8-0 #641 until October 1962, when a GP9 took over. The Illinois Central ran some of their big 2500 and 2600 class 4-8-2's until April 1960.
Most American Class 1 lines kept a reserve off steam power, usually until 1962 or '63 and in some cases as late as 1965, to protect against traffic surges that never came, or because they weren't completely trusting of an all diesel roster. By 1961 though, it was all too clear: the steam era in the United States was over.
Photo shows N&W Y-5 class 2-8-8-2 #2110 drifting downgrade in reverse after shoving a train to the summit of Blue Ridge grade.