Nemo Bridge Area
The trails continue on the other side of the tunnel. We ended up winding our way back around an access road that was likely cut by the railroad when the tunnel was being built. This trail ended up bringing us back out on the other side of the road from where we started.
That path had some moderately tough sections with some decent sized rocks, so if clearance on your vehicle is an issue (or you just want to enjoy the tunnel again) I'd recommend using the tunnel to get back to the original side of the road.