Zigong, was formed and named in 1939 with the merger of Gongjing, a great salt-producing centre since the 7th century AD, and Ziliujing. The railway network was extended to the city in 1958, and it developed rapidly as an industrial centre in the 1960s and 1970s. Rich local deposits of salt brine and natural gas support a large and varied chemical industry; other industries include the generation of electricity, and the manufacture of machinery and fertilizers.