The latest phase of a decades-long effort to help restore California’s largest tract of tidal salt marsh south of San Francisco Bay is underway this summer, thanks to the efforts of Ducks Unlimited and its partners at Elkhorn Slough.   For years, Ducks Unlimited has partnered with the California Department of Fish and Wildlife, the Elkhorn Slough Foundation on the Elkhorn Slough National Estuarine Research Reserve to restore degraded salt marsh and surrounding habitats.   Meandering seven miles inland from the coast, the Elkhorn Slough sits at the center of California’s iconic Monterey Bay. Last century, the mouth of the sinuous waterway was relocated to create a harbor which resulted in stronger tides washing in and out of the slough. Instead of shallow salt marshes, the slough began to function as a bay.