this is now UPRR
This bridge is located south of Piedmont, and is usually known as simply "The Iron Bridge".
To get to the bridge, leave Piedmont on Highway HH headed to Clearwater Lake. You'll cross McKenzie Creek and the railroad tracks a few miles out of town. Less than a mile further, there will be a carpet/flooring store on the left. You can park there and walk to the tracks directly behind the store. It's about a 15 minute walk to the bridge.