In 1956, the Spokane, Portland & Seattle Railway ran a Farewell to Steam excursion, with the SP&S 700 pulling 21 cars up the Columbia River Gorge. In 1957, the Northern Pacific offered the last of several Casey Jones Specials. The Burlington ran Iron Horse Specials through the mid-1960s.
As far as I know, though, the Great Northern ran no farewell-to-steam runs or other steam excursions. Instead, it published this 8-1/2″x11″ brochure to commemorate its decades of steam operations. The brochure includes photos of twenty of the more important steam locomotives owned by the railroad. These ranged from the William Crooks, GN’s first locomotive, to two of GN’s best: the O-8 and the R-2.
Built in the Great Northern’s own shops, the O-8 was the most powerful 2-8-2 ever built. At nearly 78,000 pounds of tractive effort, they were more powerful than most 4-8-4 Northerns. The SP&S 700, Southern Pacific 4449, and Union Pacific 844, for example, all produce less than 70,000 pounds of tractive effort. GN used O-8s for fast freight service.
Also built in GN’s own shops, the 2-8-8-2 R-2 was one of the heaviest and most powerful locomotives ever built. Weighing more than a million pounds, they had a tractive effort of more than 160,000 pounds. This would make them the fifth most powerful piston-driven class of locomotives ever built (and two of the four more-powerful ones were unsuccessful experiments). GN used them for drag freights, meaning heavy trains pulled at relatively slow speeds.
An oddity in the brochure is the Z-class 4-6-6-4 Challenger. These were designed for the Northern Pacific and built for NP-GN subsidiary SP&S. To get GN trains from its main line in Washington to its California branch, GN and SP&S had a locomotive equalization agreement for running trains over the SP&S between Spokane and Bend. As a part of that agreement, GN took over the payments on two of the SP&S Zs, then resold them back after about a decade. They were maintained and operated by the SP&S over SP&S tracks, so really were Great Northern in name only.