An ancient 130-acre California salt marsh was filled, drained and turned into an airfield; a century later, crews removed 230,000 cubic yards of soil to let the tides return

Looking at Crissy Field now, it is hard to imagine that this tranquil stretch of the San Francisco waterfront was once filled with concrete, landfill and military facilities. Families picnic on the lawns, cyclists ride the waterfront trail, birdwatchers scan the marsh and children play near the bridge.

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