Very possible they never used subs as cabs on the Peninsula, but I do recall seeing more than one freight leave Newhall with a sub rather than a caboose. I grew up about 100 yards from the Newhall St. crossing, which was closed in 1959.

I believe that in one of Signor's books there is a photo of a sub on the rear of a freight crossing the Suisun Bay Bridge. It would also not be beyond reason that they were deadheading crews in them.