Originally determined eligible by the Keeper of the National Register in the Caltrans 1985 Historic Metal Truss Bridges in California Thematic Resources study; it was listed on the National Register in 1989 as a contributing element of the Lewiston Historic District. The bridge is the second highest scoring bridge in the survey population and the highest scoring of the Baltimore Petit trusses.
The Trinity River Bridge is an unmodified example of a single steel, Baltimore Petit through-truss span with pin connections. There are steel girder approach spans on either side of the truss span, and a wood railing runs the entire length of the bridge. It is also the longest of the three existing Baltimore truss bridges built in California.