rusty - Let me see if I can help you here. Deer Creek empties into the Susquehanna River on its west shore (Harford County). I'm pretty sure I know which span you are talking of, as I have walked across it many times to go fishing at the point. That bridge, however, isn't concrete, but a plate girder design.
Now, across the Susquehanna on its east shore (Cecil County) is where the Octorarro River flows under a high 3-4 arch concrete viaduct, that is still part of NS PORT ROAD. It is made even more interesting, as the ol' PB&W (abandoned) crosses thru one of it's arches on an antique through truss bridge.
Unfortunately all of my pictures are slides, and I haven't been back up there with a digital camera. A lot of foliage around it now,would make views difficult at best, so better to wait til late fall.
I believe the former Octorarro Railroad is being operated by the WILMINGTON & WESTERN RR along the Maryland/Delaware line. Hope this helps some.