There were four narrow gauge lines in the Black Hills. The C&NW sg came into Deadwood from the north, then had narrow gauge to the mining areas.
The Deadwood Central ran from Deadwood to Terry and Portland Jct.
The Black Hills and Ft. Pierre was built by the Homesteak mine from Lead to Piedmont.
Both these were taken over my the Burlington and run untilthey were abandoned in 1930.
The last was the Warren & Lamb lumber co. which bought some of the CB&Q rolling stock when it was abandoned.
Two books are "Railroads of the Black Hills" by Mildred Fielder. Another book is "Making the Grade, a Century of Black Hills Railroading" by Rick Mills 1985.