The classifications given by railroads to their steam locomotive fleets were as varied as the machines themselves with several different designations within a particular class! Spokane, Portland and Seattle steam locomotives were likewise distinguished by wide range of classes from A to Z. In any event, the information here is most certainly not a complete, all-time listing of the SP&S's steam fleet and also is merely meant to list the general types of steam locomotives operated by the railroad.
The Spokane, Portland and Seattle Railway may have been a small railroad in terms of its actual size but it served as an important link for its parents, the Northern Pacific and Great Northern, into the gateways of Portland and northwestern Oregon. The little bridge line also was well liked in the many communities it served, one reason of how it obtained its slogan, “The Northwest’s Own Railway.” The SP&S was never an independent company and was expressly created to ferry traffic back and forth for its owners, which it did quite well for over 60 years. While the railroad did have its own identity and played an important role it never operated any of its own passenger trains and its parents always determined its direction. In the end it was folded into the merger of the NP, GN, and GN-controlled CB&Q in 1970 to form the Burlington Northern, the largest western railroad of its time.
While the SP&S often received merely second-hand equipment (2-6-0s, 2-8-0s, etc.) from parents NP and GN it was given a small roster of 4-6-6-4 Challengers and 4-8-4 Northerns beginning in the late 1930s. While none of the articulated steamers remain preserved today for still to do including a 4-8-4 Northern which is operational.
Class A-1
The SP&S's Class A-1 included its roster of 0-6-0 switchers.
Class C-1
The SP&S's Class C-1 included its roster of 4-4-2 Atlantics.
Class D
The SP&S's Class D included its roster of 4-6-0 Ten-Wheelers.
Class E-1
The SP&S's Class E-1 included its roster of 4-8-4 Northerns.
Class F-1
The SP&S's Class F-1 included its roster of 2-6-2 Prairies.
Class H-1
The SP&S's Class H-1 included its roster of 4-6-2 Pacifics.
Class L-1
The SP&S's Class L-1 included its roster of 4-4-0 Americans.
Class M
The SP&S's Class M included its roster of 2-6-0 Moguls.
Class N
The SP&S's Class N included its roster of 2-8-0 Consolidations ranging from Class N-1 to N-7.
Class O
The SP&S's Class O included its roster of 2-8-2 Mikados ranging from Class O-1 to O-4.
Class Z
The SP&S's Class Z included its roster of 4-6-6-4 Challengers.
For more reading on the Spokane, Portland & Seattle Railway you might want to consider North Bank Road: The Spokane, Portland and Seattle Railway from John Gaertner. The book is very well done and gives a general, yet articulate, history of the railroad. If you are a fan of the SP&S and/or would like to learn more about it I'm sure you will enjoy Gaertner's book!
Also consider Perfecting the American Steam Locomotive by author J. Parker Lamb. As the name implies the book details the earliest history of steam engine technology, even before it was used in railroad applications. His book later explores the development of steam locomotive technology in the United States from the 19th through the 20th centuries, covering not only the most popular steam locomotive designs but also the most successful manufactures to build them. The book has received excellent reviews and is a great resource on steam locomotives and a fine reference tool; you should find it very useful. If you're interested in perhaps purchasing either (or both) of these books please visit the links below which will take you to ordering information through Amazon.com, the trusted online shopping network.