Nebraska is a state on the Great Plains of the Midwestern United States. Its state capital is Lincoln and its largest city is Omaha, on the Missouri River. The state is crossed by many historic trails, but it was the California Gold Rush that first brought large numbers here. Nebraska became a state in 1867. There are wide variations between winter and summer temperatures, and violent thunderstorms and tornadoes are common. The state is characterized by treeless prairie, ideal for cattle-grazing, and it is a major producer of beef, as well as pork, corn, and soybeans. Nebraska is overwhelmingly rural, as the 8th least-densely populated state of the United States. Ethnically, the largest group are German-Americans, and the state has the biggest Czech-American population per capita. During the Great Migration, many African Americans came to Omaha.