The Black Hills n.g. lines (there were several) were very interesting. One of them even rostered several 3' gauge 4-8-0s. (That's not a typo.)
Check out the book "Railroads of the Black Hills" by Mildred Fielder. I believe it was reprinted fairly recently and seem to recall that Caboose Hobbies still has a copy for sale.
The Gazette also covered these lines in several issues a number of years ago - including drawings of the 12-wheelers. I don't have the issues handy, maybe someone else knows off-hand.
Best Regards,
Glenn Christensen