This is Volume 4 of a detailed, comprehensive history of one narrow-gauge railroad running a loop in the high county of the Rocky Mountains, Colorado.
Documentation is generously shared, with detailed Right of Way and Track Maps, profile drawings of bridges, elevation profiles, engine specifications, station listings--and on and on. Historic photographs and publication-date rephotographs communicate a true sense of what the daily operations were. The text gives human dimension to the entire enterprise.
Thank God for public libraries on this, considering the price and lack of availability. Volume 9 of the series, for example, carries a price in Dec 2013 of $1,899.33, used.
If you had to have one book that would tell you about narrow-gauge railroad operation, this would be the book, or I presume, any book in the nine-volume series.