Based on the road name, West Mail Road, I am guessing that this road was upgraded from a rural forest trail back in the depression era of the 1930s when rural mail delivery was vastly expanded, and depression era jobs programs made such projects possible. The original bridge was most likely a narrow one-lane timber bridge, or perhaps had a very light duty steel truss span. Such a bridge would have been obsolete by the 1960s when the current bridge was built.
The current Scotts Bridge is a very basic structure. The first construction work would have been to drive piles in at the ends of the bridge and for the wing walls. Timber was placed behind the piles, and the roadway was built up. From there, beams were placed across the span and the deck was poured. Finally, light duty guard rails were installed, and the bridge was opened to traffic. At some point, the highway was paved or seal-coated. The new surface was also applied to the bridge deck, which is kind of unusual. Normally, a concrete bridge deck is not paved over.
The photo above is a view looking northwest down the length of the bridge deck from the center line of West Mail Road. Note that the railings and guardrails are painted a pastel yellow color, which is a welcome change of pace from the more typical silver color.