If you can determine the company and regimental number on the haversacks, the details of the post might, at least, be estimated.
If the number is the 8th US Infantry, their deployments were - until at least 1886 - in Arizona and west Texas.  Since specific posts during that period were by company or companies, the actual post may never be known for sure.  Since this date would be 1894 or later (right?) the post might still be somewhere in the southwest, but could be narrowed down if a regimental association exists somewhere.