I see you have been exploring Lovejoy's Mile. That's the section of track torn up under orders of D&RG president Frederick Lovejoy during his feud with Palmer.
I don't have anything to add about this specific bridge. I was as surprised as you were to see those early iron-and-cement piers for an iron bridge. However as early as 1884 the bridge & building foremen in Utah were begging the D&RG to install iron bridges in place of most of the wood pile trestles, but the Lovejoy-Palmer fight prevented this. Obviously one single bridge was built but no others. After the D&RG and D&RGW parted ways the idea was nixed until the standard gauging of the RGW.