One thing about bridges, you sometimes have to look underneath.
The underside of a bridge is not normally the most attractive part of the structure. It does not generally feature portal bracings, ornamentation, plaques, finials, and other cool stuff. But, by looking underneath, you can often get some good clues about how the bridge functions.
To use concrete bridges as an example, sometimes it's hard to tell a tee beam from a slab from a concrete through girder without looking underneath. I have found that sometimes even the National Bridge Inventory gets the structures confused.
Without looking underneath, my suspicion is this is a wooden bridge with some steel stringers underneath. A very high percentage of old bridges, including wooden bridges, have steel stringers underneath.
Except you can very clearly see where the I-beam's flange joins the web (vertical).
https://en.wikipedia.org/wiki/I-beam
The bridge also appears to be in similar construction as another nearby bridge, which is clearly an I-beam span as well https://commons.wikimedia.org/wiki/File:IMG_4193_Magalloway_...
Looks like an I-beam to me. I can't tell if it's the older style or the Bethlehem Style.
Looks like an I-beam flange to me.
Looks like a steel stringer to me. Also the wikimedia page mentions steel.
What I'm seeing is a dirty I-beam flange with a wooden deck casting a deep shadow.
In any case, your notion that wooden bridges haven't been constructed recently/almost all non-covered examples being gone is false.
Hundreds still exist, and they continue to be built http://www.bec.iastate.edu/timber.cfm