The San Francisco Bay area boasts one of only two coastal saltworks in the United States. (The other is near San Diego.) What makes this area ideal for salt making: is a combination of shallow topography, clay soils, and Mediterranean climate - just enough rain in the winter followed by a long dry season of steady breezes and summer sunshine.
First stop on our tour of Cargill’s 12,000 acre system is the intake pond -- the beginning in a series of evaporation ponds (sometimes called concentrators or concentration ponds). This is where we pump bay water into our pond system. San Francisco Bay water is only 71 percent as saline (salty) as sea water: it contains 2.5 percent sodium chloride, vs. the ocean's 3.5 percent.
The intake pond, like all our salt ponds, is surrounded by low-lying levees, or walls of dirt that separate it from the Bay and other ponds. These levees, which trace historic property lines and shoreline features, have shaped our baylands for more than 100 years. Most were built in the late 1800s to reclaim marshland for agriculture and then salt making. Today, they're maintained by our wooden dredge, the Mallard II.
The Mallard II
The Mallard II has plied San Francisco Bay's salt ponds since her keel was laid in 1936. The crew of the Mallard II works year-round, maintaining about 10 miles of our 80 miles of levees per year. The one notable exception: when the Mallard II heeded the nation's call during World War II, retrieving artillery shells from the Bay floor around Mare Island and Port Chicago.
Anchored on her spuds, or stabilizing legs, the dredge scoops mud in her clam-shell bucket from borrow ditches within the salt ponds, and places it atop the levees. The Mallard II not only preserves the levees, which are subject to wind and wave erosion, but helps maintain a network of gates, pumps and siphons that move brines through the system of evaporation ponds. Let's follow!
Roughly 8,000 acres in the South San Francisco Bay are devoted to salt evaporation ponds – and all of their habitat is protected by the Don Edwards San Francisco Bay National Wildlife Refuge. Evaporator ponds and the marshes that surround them provide important habitat for more than 70 species of birds, including several endangered species. Because the ponds are shallow - an average of 1.5 feet deep - it's easy for shorebirds and waterfowl to find a meal in the low- and mid-salinity ponds.
Flying over the bay or driving over some of the area's bridges, you will notice that evaporation ponds have distinctive colors: beautiful green and red hues, colored by the microorganisms that thrive at varying salinity levels. Learn more about the unique salt pond colors.
As the water naturally evaporates, the brines become increasingly salty, and we circulate them through our salt pond system so as they get saltier, they get closer to our crystallizer beds.
When the brine is fully saturated, we call it "pickle." At this point, the brine is holding as much salt as it can, and salt begins to crystallize. Our watermen pump the pickle into large crystallizer beds. Here, the brine will undergo its final transformation, yielding pure salt crystals. This is where the art and science of salt making are put to the test. If the days are too hot and the breeze is too gentle, small flakes called "drift salt" can form - to avoid that, our watermen may add brine to the crystallizers. On the other hand, untimely rain could dilute the brine and delay harvest for weeks - even a whole season.
After five long years of gentle coaxing, the brines have yielded a crop of beautiful salt crystals. The first step in preparing for harvest is draining off the red "bittern," a solution of other naturally occurring minerals that has concentrated during the evaporation process. Bittern, which is high in magnesium, is a valuable tool for road safety. It is used as a low-corrosive de-icer during the winter, as well as a dust control agent for vineyards and country roads in the summer months.
Now the bed of salt – 12 inches deep and glistening in the California sun - is ready for harvest. It's already 99 percent pure. We're in a race against winter rains and work 20 hours per day, five days a week, to collect salt from the crystallizer beds. Our mechanical harvester rips through the rock-hard salt and scrapes up the pieces with a blade that operates something like a snowplow. The salt is carried onto a conveyor then loaded onto giant haul trucks that drive alongside the harvester. Each haul truck carries approximately 30 tons of raw salt to the wash house.
At the wash house, the salt is poured into a saturated brine wash. Because saturated brine is already carrying as much salt as it can hold, very little salt dissolves in the wash.
The slurried salt is moved through a series of washers and augers, then dropped onto a massive conveyor that carries it 1/6-mile to the tip of our gantry -- a height of 90 feet -- where it is poured on top of our salt stack.