Thank you to Montezuma Yardmaster and to Tom M . as well in reference to your previous comments.
First off, I'd say that in 1939 there was probably a minimum of 50+ trains per day, most of which started and ended their runs at the famous Oakland Pier terminal (Mole)..
This doesn't include electric suburban trains, ferryboats and misc other entities. My feeling is that the other railroads in the area (WP, ATSF, etc) "might" have sub-contracted with SP to have their laundry done at West Oakland as well...
Yes, I have also heard about THIS laundry being the largest industrial laundry in the World.
The former/current building used by AMTRAK referred to as the old laundry building is NOT the same place. The one I speak of was located nearby but torn down many years ago.

I visited the original laundry building several times as a young boy during the many times I rode around with SP "water service gangs" in those big, orange SP trucks. But I think I was only in the building once or twice when operations were in full swing. A very impressive place. Especially seeing all the women working upstairs with dozens of sewing machines.
Somewhere in the photo archives at CSRM or the UP museum photo archives, there must surely be interior photos of this amazing place. Maybe someday they'll surface for us to enjoy.

KRK