The Dec Trains magazine has an article about experiences firing on the ATSF. The pic (of a 2-10-2) jogged my memory about a question I've long had about ATSF tenders: Some have a large housing on top of (or sometimes behind?) the oil bunker... looks to stand about 4-5-ft high, the top of which is arched. In a couple pics I've seen, they appear to have access doors. Only thing I could come up with is that it's part of a bunker oil heating system. Anyone ideas?