The car is Great Western Railway (Colorado) caboose 1002. Built in 1906 (or at least acquired by the GWR in 1906), sold to the Black Hills Central in 1963 for $400.00. Why it has what appear to be D&RGW cast tender steps on the platforms is anyone's guess, though photos show it with them since at least the early 1950's.
Below is a letter from the GW to the Black Hills about selling the caboose;
Further letters show that it took the GW until December 15, 1963 to have the car ready to interchange with the C&S and it presumably made it to Hill City on its own wheels.
Neat car, the GWR is, in my opinion, an underappreciated bit of Colorado railroad history.
Jason Midyette