After the gold rush, demand for salt soared for ore refining, livestock raising, paper pulping, and food preservation. Many former gold-seekers, including Swedish immigrant Andrew Oliver, turned to producing salt by diking tidal marshland to create evaporation ponds and manufacturing salt on an industrial basis. Andrew Oliver built wind-powered Archimedes screw pumps to move salt water between the ponds, and remains of some of these wooden pumps survive at Pond 14 in the Eden Landing Ecological Reserve. The Oliver family prospered by expanding production and buying neighboring salt companies, then sold the enterprise to the Leslie Salt Company in 1931; it later became part of Cargill Corporation in 1978. In 2003, state and federal government acquired most of Cargill's South Bay holdings, and the more than 15,000-acre purchase became the South Bay Salt Pond Restoration Project, one of the largest ecosystem improvement efforts in history.