Bruce, because of the rivets it was probably made in the first half of the last century. I see that at the end that it has been taken away from the construction by a cutting torch. I don't rule out the possibility that it may have been part of a bridge.
I'm curious if this is correct or not.
I therefore hope that you can provide us with a solution to this puzzle in due course.
Intriguing photograph though, Buddy!

I really like the treatment you used here, and very apt title. tigs=^..^=

You're funny Bruce, really like treatment to this wonderful image. That would have to be for a huge building structure or bridge

Well, I Googled Point San Pablo Harbor, viewing a satellite photo of the area, and am not seeing a bridge or an abutment of a removed bridge, but I see several industrial spots, including round water or fuel tanks and a harbor area on the western shore of the point. Considering the formidable size and thickness of this piece, I would suggest it is more likely to be a remnant of a dismantled structure originally in the harbor. I find it more likely by seeing, in the far upper left corner of the photo, how close this spot is to the water. Some may think of this capture as being too mechanical for their taste, but I always enjoy having the opportunity to closely study and interpret shots like this. So you get a couple thumbs up from me, Bruce.

Orrrrrr, maybe I*m just weird.

-nik