The basins of the Yellow and Yangtze rivers are separated in the west by mountains, which give way to hills and finally disappear altogether in the flat land of the east coast. The two basins are quite distinct, when it comes to farming. Dry farming of wheat and millet characterizes the Yellow River basin in the north; irrigated rice agriculture predominates in the warmer and wetter basin of the Yangtze. In the extreme south is the valley of the His or West, River, an area of mild climate and fertile soil that would later form the southern boundary of China.