Many of these Chinese men came from the Pearl River Delta Region in southern China, where they had learned how to develop fertile farmland in inaccessible river valleys. This know-how was used for the reclamation of the extensive valleys of the Sacramento-San Joaquin River Delta. During the 1870s, thousands of Chinese laborers played an indispensable role in the construction of a vast network of earthen levees in the Sacramento-San Joaquin River Delta in California. These levees opened up thousands of acres of highly fertile marshlands for agricultural production. Chinese workers were used to construct hundreds of miles of levees throughout the delta's waterways in an effort to reclaim and preserve farmland and control flooding. These levees therefore confined waterflow to the riverbeds. Many of the workers stayed in the area and made a living as farm workers or sharecroppers, until they were driven out during an outbreak of anti-Chinese violence in the mid-1890s.