I don't know Pittsburgh, but I think industries are almost the same all around the globe. So here is my proposition:
For me this open space looks just perfect for a receiving/dispatching yard for trucks - something which you hardly ever see on a model RR layout. In most cases the turning space for trucks on a layout is way too small, so that you really couldn't turn a 18-wheeler around. But your space looks just right. So I would cover the whole place with somewhat patchy concrete or asphalt or even gravel and dirt, with some weeds growing here and there. And of course you can install some piles of boxes, crates, planks or whatever (as long as you still can turn those rigs around
)
You could define the spur as a team track. I would also install a gantry crane across the track so that you can unload heavy machinery from a flat car.
As a last idea: I would rise a chain link fence around the property (with KEEP OFF and NO TRESPASSING signs) and perhaps a scale house near the gate.
Ron