So the question is when was this built exactly, and where did it come from originally?
Based on style, the bridge is much older than 1976. 1920s or 1930s for example... Iowa continued to build bridges with under 20 foot roadways later than many states. The 1976 date is either an error, or refers to a relocation of this bridge to this location, or a rehabilitation of the bridge.
When were rivets last used in truss construction? Could this bridge have been built before 1976?
Spot on Nathan... I was thinking about 1925 give or take.