The Ace Train goes by quite a few salt evaporators by the bay.  It makes it look like the train is running right through the bay (it sort of is) especially when you see the train from 680.  The train can be seen when traveling north bound on 680 in the Scott Creek to Mission area if you know when to look (and are not the driver).  Each evaporator is at a different stage and concentration level.  According to one web site (linked below) the process take about 7 years first letting salt water in from the bay.

There used to be several salt factories in the Bay Area.  I believe this is the only one left.  It is owned by Leslie Salt, which was bought by Cargill in the late 1980s.  A deal is progressing where Cargill will sell 16,500 acres of the salt evaporators to the state and federal government to be turned back into wetlands.  Salt will still be produced at the factory, using fewer ponds.

Links:
How Salt is made.  San Francisco Bay Bird Observatory web site.

Leslie Salt Facility.  One of the salt evaporators is in the foreground.  Taken toward the West, while passing the facility.

Overlooking a much larger evaporator with the salt piles in the background.
Taken in the morning after passing the facility, looking to the North West.

Almost the same angle on the return trip that evening, with rain clouds overhead.  The Dumbarton Bridge would be to the left, not quite visible in the picture.  It is north of the salt facility.

Conversation overheard on the Ace Train:

Person A:  "That's how they make the salt?  I'm never going to use (brand) salt again!"
Person B:  "What, do you think the other companies make it in a clean room?"
Person A:  "Oh. I guess you're right".

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Ace train icons by Don's Depot.