Jon,
Good link ! What surprises me is that none of these railroads are mentioned in George W. Hilton's "American Narrow Gauge Railroads"!
The railroads mentioned are: The Ahukini Terminal and Railroad Company, Kauai; the Kauai Railway, kauai; and the Harbor Springs Railway, Harbor Springs,Mi.
3' gauge is the most popular, 3'6" next, then 2'. After that it's a toss up 2'6", 3'2", 3'61/2", 3'4", 4'3".
One quote from the book," Hawaii was the capitol of 30" gauge, as Maine was for 2' gauge.
Pete