Erik,
The main ore hauled down from Monarch was limestone which went to the big CF&I steel factory in Pueblo. In the narrow gauge days the cars would transfer loads to std gauge gons via the barrel a large contraption which turned the ng gons upside down to empty them this was in Salida. In 1956 the line was standard gauged and remained in service up until 1983. I still remember seeing a few trains on Monarch as a small boy in the early 80's. Would have made a nice excursion line, but the grade are a firm 4.5%. Hope this helps answer your question.
William
aka drgwk37