The book at the depot that I was thinking about is the one Dan mentions. There was also an edition of the Western Railroader that had an article on the Sumpter Valley by Mal Ferrol. I think this article predated Rails Sagebrush and Pine. I once had a copy, but shared it around and it evaporated. A freind sent me a copy, but the postal service lost it. Oh well!
Another neat article is one that appeared back in the 1970's I believe in the NMRA Bulletin entitled "Sumpter Valley-1000 Mile Long and A Yard Wide Dream, by Don Daughs. It has some real neat original source information as he was a railroader with Big Creek and Telocasset during the time SVRy was operating. He shares a number of stories that won't be found anywhere else.
Also some other model magazines have had articles.