Substructure does not appear original and construction date is suspect for alteration/relocation. That said, the riveted angles you note appear to be beam stiffeners, not hangers. Unless I missed something in your photo. My feelings is this is a railroad-designed highway over railroad bridge that may have been relocated/improved in 1911. But that's just based off cursory review of your photos as shown here.
Bridge looks to be a relocated lightweight railroad pony truss span, reused for road use. The evidence is in picture #24, where there are unused pieces of angle iron, which may have connected the former railroad stringers. The Santa Fe archives reports that this bridge received a completely new deck in 1929, so it is possible that the other railroad related components would have been removed then as well?
Is BNSF expanding underneath this and the through truss? It seems odd that they removed both trusses in one year. I'm hoping thats not a bad sign for the other overpasses further east..