I guess time is a relative matter. The D&RG arrived in Silverton in 1882, the SR started 7 years later and their Silver Lake Branch dates from property acquisition in 1895. The Silver Lake Branch became part of the Silverton Northern much like the SG&N later became the Gladstone Branch of the SN by the time the 1920 ICC maps were drawn. And I have no evidence of the D&RG going "way past" the SG&N engine house--the evaluation maps indeed show one track owned by the D&RG going a little past the SG&N facilities but there is Cement Creek in the way to go too much further.
The buidling with the smoke stacks is puzzling, but the building in front of it with the shed roof addition was the office for the SG&N. A really nice photo of this building is in the Rainbow Route with an engine on the in street track next to the building. I found this photo in my house when I first moved in and donated it to the historical society.