Caption
A glance out of your airline window while landing at San Francisco International Airport will reveal a patchwork of vividly-colored salt evaporation ponds. The salt ponds support a five-year-long process of solar evaporation that yields 600,000 tons of salt a year. As San Francisco Bay water makes the trip from 3% to 30% salinity it evolves through a succession of bright colors. These are evidence of halophilic algae, bacteria, and other organisms that thrive at specific salinities.
The salt evaporation impoundments cover what was once a vast marshland. In the mid-19th Century small “mom & pop” salt operations were established only to be subsumed by several waves of corporate consolidation. In recent times all 100,000 acres of San Francisco Bay salt ponds were owned by one company – the Cargill Corporation. A couple of years ago Cargill sold 15,000 acres of salt ponds to a coalition of non-profit and government agencies to manage for the public good with an emphasis on wildlife habitat, flood control, and recreation. Some of the ponds are destined to become tidal marshland again.
The salt pond geometries reveal aspects of the landscape’s history. In the image above, taken just west of the Coyote Hills, you can see an oddly shaped pond that maps the former path of the Coyote Hills Slough. This slough was once navigable and formed the border between the municipalities of Hayward and Newark, California. The stream itself was relocated long ago to the straight-lined flood control channel seen to the north but its former winding course still serves as a political boundary.