Very cool shots, Aaron...that barn being completely overgrown like that kind of gives away it's age...
Those concrete buildings remind me of the "job" buildings we have out here, that date back to the turn of the century till about the 30's or so. Near tunnels, road projects and smaller dams, you can often see the remains of concrete buildings that housed machinery, shops and blasting supplies. In the case of a "powder shack", it'll have a single, small door with a low header, no windows and at least one opening/vent at or near the peak.
If you say these buildings are near the train tunnel, my guess would be that these are remnants of that project.