Brian,
By inspection of google maps, it appears the trestle in question likely connected to the east to a rail yard which is oriented in a northwest/southeast fashion. Note where the present rails cross E. 15th St to stub end a few hundred feet before the channel. The photograph appears to be looking south/south westerly. The rail line which splits off inland is also visible in google though it now appears to be severed. I also googled
Northern Fish Company (est 1912 and now known as Northern Fish Products) and their main page features a slide show. Two of the photos possibly show part of this scene. One clearly shows an elevated trestle (the pic with the two old trucks) and the other shows a rail bridge with buildings which say "City Dock" in the back round looking towards the west?
Anyone else care to comment or correct me?
Steve, awesome photo and thanks for posting.