From Wikipedia

The Dust Bowl

The Dust Bowl or the Dirty Thirties was a period of severe dust storms causing major ecological and agricultural damage to American and Canadian prairie lands from 1930 to 1936 (in some areas until 1940). The phenomenon was caused by severe drought coupled with decades of extensive farming without crop rotation, fallow fields, cover crops or other techniques to prevent erosion. Deep plowing of the virgin topsoil of the Great Plains had displaced the natural grasses that normally kept the soil in place and trapped moisture even during periods of drought and high winds.