This was a standard gauge Calumet & Hecla bobber caboose, built for the Mineral Range Railroad (Standard Gauge), probably number 603 as it looks identical, and sold to the C&H when they built the Traprock Valley line to their recently acquired northern properties, Allouez, Ahmeek, Seneca etc in 1925. They also purchased part of the Mineral Range line that served these mines originally, along with a few pieces of equipment including locomotives and steel sided rock cars. This picture was taken at a siding at Ahmeek, the streetcar depot can be seen in the background along with the Ahmeek bottling works. This car was replaced in 1947 by an ex Cotton Belt caboose that was donated to North Freedom in 1963 and left the property there recently. Their other caboose, #2, was built for the Copper Range, and was sold to C&H in 1925. This car still exists at the Houghton County Historical Society in Lake Linden, and me and my group (Copper Range Railroad Historical & Technical Society are in the early stages of restoring it.
The line was converted to standard gauge in 1907, with small portions of it staying 49" gauge until around 1920. The reason for the odd gauge was an order screwup in 1867, not knowing the difference between inside and outside of flange measurements. This was for their first locomotive, the "Fluke", which nobody seems to have any information about.