This link may be of interest to those who enjoy railway engineering or structural modeling. The Camas Prairie RR would seem to qualify as an "honorary narrow gauge". Link leads to a Library of Congress file with 126 B&W images detailing impressive trestles, tunnels and trackwork on the Camas Prairie 2nd subdivision, mostly taken ca. 2002.
The CSP 2nd sub. operated in west-central Idaho until abandonment in 2000. From Port of Lewiston (ID) the line rose 3000 feet in elevation. These pictures were taken ca. 2002, after abandonment. At the present time, 50+ miles (Spalding to Craigmont) remain in place including the most scenic portion and most of the large trestles.
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memory.loc.gov]