Rich mentions the Nacozari. That was perhaps the last "regular" use of standard gauge steam. As noted above, the SP ng. ran steam after that. And then there were the movie trains, flood trains, various specials, and so on. I have a long list of various "last runs" that I prepared 40 years ago but why dig it out because too much depends on definition. And some new "last runs" have surfaced since then.

What I think would be far more interesting would be an overall view of the progressive demise of steam on the SP system, perhaps by division. How did SP manage the transition from steam to diesel. Does such an animal exist anywhere? It may be sitting on my book shelf, unread or forgotten. Tom, do you have that info? What divisions dieselized first, how was it done, and so on. Just to complicate things, I suspect some nominally dieselized areas probably saw some occasional steam visitors as power was moved around, peak needs, etc.

JBWX