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! Southern Pacific steam locomotives were likewise distinguished by a wide range of classes from A to T. In any event, the information here is most certainly not a complete, all-time listing of the Espee's steam fleet and also is merely meant to list the general types of steam locomotives operated by the railroad. Also, this data only covers SP's "modern" steam fleet. For information regarding its roster prior to 1900 please click here.
Much like the Pennsylvania Railroad was to the State of Pennsylvania so was the Southern Pacific to the State of California, an institutional icon. Also just like the Pennsy the Southern Pacific (also referred to affectionately as the “Espee” by railfans and historians after its SP reporting marks) has such a history that entire libraries of books could be written on the differing aspects of the railroad. The SP was by far our country’s single largest classic railroad (i.e., before the modern-day merger movement began in the 1950s), spanning over 15,000 miles and reaching from the stretches of northwest Oregon to southeast Louisiana!
The Southern Pacific's steam fleet was just as celebrated and vaunted as the railroad itself. It rostered massive steamers like 2-8-8-2s and 2-10-2s, including its famed Cab Forwards, all of which were articulated and used to drag long freights over the Sierras. Its fleet also included the beautiful, streamlined 4-8-4 Northerns, known as Golden States by the SP, used to haul passengers in its Daylight trains while skirting the southern California coastline. Today, happily, no less than 65 Espee steamers remain in some state of preservation (the most of any, one single railroad) with no less than nine still operational (including famed Golden State #4449) and many more under restoration!
For more reading and background on the SP consider the books Southern Pacific Railroad from noted author Brian Solomon. The book gives a superb general overview of the railroad and its extensive passenger operations and is filled with excellent photographs (many in color) of the Espee. If you are a fan or have any interest whatsoever in the Southern Pacific you will very much enjoy the publication.
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.