It looks like the 1938 Santa Clara River bridge, the last remaining structure along the 1939 Newhall-Saugus Bypass will be replaced. Not terribly surprising in that town, considering how much development has occurred in the area. The new bridge will be a bit wider, with sidewalks. The parallel 1968 bridge is also being widened at the same time. The idea is to join the bridges and create a more seamless roadway. While I already have photos, I plan to do a full photo shoot in the next couple weeks, assuming it doesn't rain on the weekend I can go.
For the location and what the structures look like today: