Cattle towns such as Abilene have long since given way to manufacturing centers. Wichita turns out 70 percent of the general-aviation aircraft produced in the U.S.; Kansas City makes automobiles. Among the top states in crude-oil production, Kansas also banks on one of the nation's largest natural gas fields. Salt deposits near Hutchinson are the remnant of a shallow sea that once submerged the Great Plains. Although no other state grows more wheat—Mennonites from Europe introduced a hardy winter variety in the 1870s—livestock earns more for Kansas.