"Nature is almost everywhere," wrote environmental journalist Emma Marris in her buzz-generating 2011 book Rambunctious Garden: Saving Nature in a Post-Wild World. " But wherever it is, there is one thing that nature is not: pristine."

Humanity's imprint is unavoidable, even deep in the backcountry. Smog frequently blankets Sequoia National Park, yellowing the needles of ponderosa and Jeffrey pines, and slowing their growth. Nitrogen pumped into the atmosphere by power plants, farms and cars has changed the chemistry of lakes in Rocky Mountain National Park. There are few places on Earth where the buzz of planes and cars isn't, at times, audible. Almost every Western river of any magnitude has been dammed. And then, of course, there's climate change.

Welcome to the Anthropocene, the "age of man." More than a decade ago, atmospheric chemist Paul Crutzen popularized the term, arguing that this new epoch dawned as early as the late 18th century. "A long-held religious and philosophical idea -- humans as the masters of planet Earth -- has turned into a stark reality," he wrote recently on Yale Environment 360.

But though "pristine" wilderness may have vanished long ago, nature persists. It's all around us, in city parks, in national parks, on our farms and in our gardens. And we can care for it without leaving it alone. As Marris wrote in an online New York Times debate last year: "We have a choice. We can write the whole planet off as irrecoverably ruined, or we can redefine 'good' and 'bad.' And this is where it gets tricky. What 'good' replaces pristineness? Biodiversity? Ecosystem services that benefit humans? Beauty?"

These aren't just lofty questions for ivory-tower thinkers. As Nick Neely reports in this issue's cover story, scientists and land managers are grappling with them in concrete ways as they undertake the most ambitious wetland restoration project on the West Coast.

San Francisco's South Bay is one of the most invaded aquatic ecosystems in the world.  Industrial salt ponds have all but replaced wetlands. Yet wildlife -- both native and non-native -- has survived and even thrived in this altered landscape in surprising ways. Threatened snowy plovers, displaced from other coastal habitat by human activity, have taken refuge there. So have California gulls. (Their arrival, as you'll see, has its downsides.) The endangered California clapper rail, meanwhile, has hung on thanks partly to invasive grass that has squeezed out native flora.

Now, thousands of acres of salt ponds are being reopened to the tides. It's a messy, uncertain process, rife with tough choices. The Bay will eventually become a new version of its old self. It won't be pristine, but it will still be wild and unpredictable. And in the process, it may be redeemed, as a fundamental natural process  -- the rise and fall of the tides -- is finally allowed to exercise its influence again, alongside our own.