4behind2 is spot on. Those are the old temporaries and judging by the lack of plastic pellets on the ground, I'd say before my time but after the tower closed, so very late '80s until mid '90s. Nailing down the exact time could be done if you had the old General Notices for track work projects where Bliss would be re-opened, maybe for the big Harold project in the early '90s.
When they did it in my time, they would have 2 temps out there, one for each track. I wondered why we had 2 when we so rarely wrong-railed, but then the drilling would start and the second one was a big help.