In a hotter climate, dirt is a hot commodity. With sea levels expected to rise 3 to 6 feet by the end of the century, coastal communities are moving fast to construct major shoreline projects to protect themselves. As the size of these projects expands, the primary building materials — dirt and mud — are getting scarce. … [Parts of San Francisco Bay were] once used for industrial salt making, and giant evaporation ponds were built here more than a century ago. Now, its marsh habitat is being restored as part of the Eden Landing Ecological Reserve. The old salt pond levees still stand between the bay and hundreds of thousands of people on the shoreline. But waves and weather have eaten away at them.