Vast stretches of industrial salt ponds are slowly creeping back to natural, wildlife-friendly state.

Fly over the southern finger of the San Francisco Bay and you’ll encounter a bizarre sight: vast pens of vividly colored water, some rusty like Martian soil and others as deep crimson as slaughterhouse blood.

These are the region’s productive salt ponds, which Matthew Coolidge of the Center for Land Use Interpretation once described to CityLab thus:

“Salt is a funny thing,” says Coolidge. “It’s one of the most basic things in our food industry, yet it doesn’t come from many places in the United States.” Some of it is mined, like from a big rock-salt deposit under Detroit; and some comes from evaporation ponds like these guys, which together make up the nation’s largest salt-pool system outside of the Great Salt Lake.

A network of dykes operated by Cargill Salt holds the water in place as crystalline material accumulates on the bottom of the ponds. “Then they come in with these big graters that just scrape off the top layer, put it in a pile to process, and turn it into various-shaped globules ranging from pea size to small grains,” Coolidge says. Most of the salt goes to the chemical industry or roadway deicers, with only 3 percent winding up as food seasoning. The entire process can up to 5 years to generate commercially viable salt.

Courtesy of Around the Bay: Man-Made Sites of Interest in the San Francisco Bay Region

The Bay Area was not always home to these inflamed-looking basins, which acquire their unusual coloring from halophilic bacteria. It wasn’t until the Gold Rush that salt speculators really began transforming the land; before that the shoreline was verdant marshes rippling with fish, shellfish, seals, and a chirping horde of shorebirds. And it’s slowly creeping back to that primal state, thanks to the 2002 South Bay Salt Pond Restoration Project.

That year, Cargill handed over more than 15,000 acres of salt ponds to various state and federal agencies for massive wetlands restructuring. The project’s success so far is visible in this fantastic comparison of satellite images put together by NASA. Whereas up to 85 percent of the shoreline was once occupied by industrial-salt concerns, now big stretches of weirdly hued, inhospitable terrain are again becoming green and inhabited by new wildlife.

Here’s the view from September 2002:

NASA/USGS

And the same perspective from October 2015:

NASA/USGS

The space agency—which has made an image-comparison tool that’s worth checking out—highlights the nearly 3,000 acres you can see devolving back into natural marshes:

On the far left side of the image, the bright, gypsum-covered salt flats of the Ravenswood Pond Complex (around the Dumbarton Bridge) underwent a hybridized restoration over 13 years. Bay waters were returned to some ponds (turned from white to dark green), while others were left as salt flats because a few bird species have adapted well to the area over the 160 years of salt production. And in one area (visible just east of the bridge), artificial mounds and miniature islands were constructed to provide habitat for certain species (snowy plovers, for instance) amidst a landscape that has been returned to tidal water flows….

Walking around the south side of the Bay (the Alviso Pond Complex), old salt evaporation ponds have started changing colors from white and tan—or bright green—to darker greens and muddy browns. The brightest areas are flats where salt-encrusted mud was dried out by the air. The shades of green and brown in the various ponds and flats can be attributed to different levels of salinity, different depths of water, and different types of algae and microorganisms thriving in the varied conditions. The darker the shade of green, the closer the water is to the ambient salinity of the Bay.

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