Cotton, formerly the leading cash crop of Oklahoma, has been succeeded by wheat; income from livestock, however, exceeds that from crops. Many minerals are found in Oklahoma, including coal, but the one that gave the state its wealth is oil. After the first well was drilled in 1888, the petroleum industry grew enormously, until Oklahoma City and Tulsa were among the great natural gas and petroleum centers of the world. Oil and gas have declined somewhat in importance today. Many of Oklahoma's factories process local foods and minerals, but its chief manufactures include nonelectrical machinery and fabricated metal products. Military bases and other government facilities are also important.