After lots of hot glue, photo references of the prototype, and head-scratching, here's what the area looked like before the plaster cloth went on. It's a complex area - in that first shot you can see the 3-track staging yard under the Elmer's glue - it'll remain accessible from the access hole (which is framed out here). That track is at about 52" high. Below that, at 47", is a return loop running under all of this.
Then there's the creek, coming into the scene near the speaker (yes, I know, perhaps I'll move it much later when this scene nears completion). I had to figure something interesting to do w/ it, while evoking the prototype's sense. Using the actual creek's route, I copied that and also managed to route the creek around the access hole, twisting and dropping below the town and eventually under the big 45-A trestle.
These first couple of shots are from really high viewing angles - which you can't see in real life without a ladder. But they show how the creek, access hole, and everything else fits together.
Here is a view from slightly below normal viewing angles. The hill behind this bridge is higher than on the prototype, but it's hiding the access whole. And I think it'll work pretty well - evoking the very rugged terrain as you move away from the town of Ophir slightly and down under this bridge.
The bridge, btw, is about 65% of the prototype's size. The creek twists down and exits between the two right-most foundations. These are the three heavy footings for the lower bents of 45-A - they support their own set of heavy stringers over the creek - then the actual trestle bents for the bridge above were built on those stringers.
And another fairly high-angle view, showing the creek meandering below the town. There's also a dirt road coming up the left side of the creek, crossing narrowly thru a couple of bents of bridge 45-A. There's timber retaining walls supporting this road above the creek.
If you'd like to see photos of the prototype town and bridges, I have an extensive set of details & links on my Route Summary page - just scroll down to milepost 45 or so.