massive dust storms, and several harvests were completely ruined. The experiences of the Dust Bowl, coupled with local bank foreclosures and the general economic effects of the Great Depression, resulted in many South Dakotans leaving the state. The population of South Dakota declined by more than 7% between 1930 and 1940. Economic stability returned with the U.S. entry into World War II in 1941, when demand for the state's agricultural and industrial products grew as the nation mobilized for war. In 1944, the Pick–Sloan Plan was passed as part of the Flood Control Act of 1944 by the U.S. Congress, resulting in the construction of six large dams on the Missouri River, four of which are at least partially in South Dakota. Flood control, hydroelectricity, and recreational opportunities such as boating and fishing are provided by the dams and their reservoirs. In recent decades, South Dakota has been transformed from a state dominated by agriculture to one with a more diversified economy. The tourism industry has grown considerably since the mid-twentieth century, with the Black Hills becoming more important as a destination. The financial service industry began to grow in the state as well, with Citibank moving its credit card operations from New York to Sioux Falls in 1981, a move that has been followed by several other financial companies. South Dakota was the first state to eliminate caps on interest rates. In 2007, the site of the recently closed Homestake gold mine near Lead was chosen as the location of a new underground research facility, the Deep Underground Science and Engineering Laboratory. Despite a growing state population and recent economic development, many rural areas have been struggling over the past 50 years with locally declining populations and the emigration of educated young adults to larger South Dakota cities, such as Rapid City or Sioux Falls, or to other states. Mechanization and consolidation of agriculture has contributed greatly to the declining number of smaller family farms and the resulting economic and demographic challenges facing rural towns. However, the state often ranks highly for its way of life, and Gallup's well-being index in 2018 named South Dakota the happiest, healthiest state in the United States. Geography South Dakota is in the north-central United States, and is considered a part of the Midwest by the U.S. Census Bureau; it is also part of the Great Plains region. The culture, economy, and geography