The C&S valuation Map lists it as the Stone Store Building.
I can't help but wonder if it was built by the DSP&P Land and Construction Co along with the Roundhouse and the Stone Tenements.
If you look at the C&S town plat map the mainline has to S-curve around this structure indicating to me at least, that it was sited early on with little forethought. Surely a merchant of standing would not erect a structure in the the straightline path of the newly arrived railroad at a place where there was nothing before the arrival of the DSP&P?
The other RR buildings such as the Depot, Hotel, Dispatcher's Office and Super's residence are not constructed from stone at a time when they were building towards Gunnison. The righthand corner has signage of a Lunch Room in some other photos.
The photo of Como taken by Mellens in 1883 (Pict. Supt.)is too dark for my eyes to make out the store absolutely but is present in this 1899/90 Buckwalter photo of DL&G 192.
Como Buckwalter Photo DPL
Make of this what you will,
Chris
in New Zealand