See D. Worster, Dust Bowl: The Southern Plains in the 1930s (1979); T. Egan, The Worst Hard Time (2005).
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), caused by severe drought coupled with decades of extensive farming without crop rotation or other techniques to prevent erosion. It was largely a man-made disaster caused by an abnormally severe drought combined with the deep plowing of the virgin topsoil of the Great Plains, which killed the natural grasses. Such grasses normally kept the soil in place and moisture trapped, even during periods of drought and high winds.
During the drought of the 1930s, with the grasses destroyed, the soil dried, turned to dust, and blew away eastwards and southwards in large dark clouds. At times the clouds blackened the sky, reaching all the way to East Coast cities such as New York and Washington, D.C. Much of the soil ended up deposited in the Atlantic Ocean. The Dust Bowl affected , centered on the panhandles of Texas and Oklahoma, and adjacent parts of New Mexico, Colorado, and Kansas.
The storms of the Dust Bowl were given names such as Black Blizzard and Black Roller because visibility was reduced to a few feet (around a meter). The Dust Bowl was an ecological and human disaster. It was caused by misuse of land and years of sustained drought. Millions of acres (hectares) of farmland became useless, and hundreds of thousands of people were forced to leave their homes. Degradation of dry lands claimed peoples' cultural heritage and livelihoods. Hundreds of thousands of families from the Dust Bowl (often known as "Okies", since so many came from Oklahoma) traveled to California and other states, where they found conditions little better than those they had left. Owning no land, many traveled from farm to farm picking fruit and other crops at starvation wages. John Steinbeck later wrote the classic Pulitzer Prize-winning novel The Grapes of Wrath and also Of Mice and Men about such people.
The Dust Bowl area lies principally west of the 100th meridian on the High Plains, characterized by plains which vary from rolling in the north to flat in the Llano Estacado. Elevation ranges from in the east to at the base of the Rocky Mountains. The area is semi-arid, receiving less than of rain annually; this rainfall supports the Shortgrass prairie biome originally present in the area. The region is also prone to extended drought, alternating with unusual wetness of equivalent duration. During wet years, the rich soil provides bountiful agricultural output, but crops fail during dry years. Furthermore, the region is subject to winds higher than any region except coastal regions.
Immigration began again at the beginning of the 20th century. A return of unusually wet weather confirmed the previously held opinion that the "formerly" semi-arid area could support large-scale agriculture. Technological improvements led to increased automation, which allowed for cultivation on an ever greater scale. World War I increased agricultural prices, which also encouraged farmers to drastically increase cultivation. In the Llano Estacado, farmland area doubled between 1900 and 1920, and land under cultivation more than tripled between 1925 and 1930. Finally, farmers used agricultural practices that encouraged erosion. For example, cotton farmers left fields bare over winter months, when winds in the High Plains are highest, and burned their wheat stubble, which deprived the soil of organic matter and increased exposure to erosion.
The unusually wet period, which encouraged increased settlement and cultivation in the Great Plains, ended in 1930. This was the year in which an extended and severe drought began. The drought caused crops to fail, leaving the plowed fields exposed to wind erosion. The fine soil of the Great Plains was easily eroded and carried east by strong continental winds.
On November 11 1933, a very strong dust storm stripped topsoil from desiccated South Dakota farmlands in just one of a series of bad dust storms that year. Then, beginning on May 9, 1934, a strong two-day dust storm removed massive amounts of Great Plains topsoil in one of the worst such storms of the Dust Bowl. The dust clouds blew all the way to Chicago where dirt fell like snow. Two days later, the same storm reached cities in the east, such as Buffalo, Boston, New York City, and Washington, D.C. That winter, red snow fell on New England.
On April 14 1935, known as "Black Sunday", twenty of the worst "Black Blizzards" occurred throughout the Dust Bowl, causing extensive damage and turning the day to night. Witnesses reported that they could not see five feet in front of them at certain points. The dust storms were so bad that often roosters thought that it was night instead of day and went to sleep during them.
The Dust Bowl exodus was the largest migration in American history within a short period of time. The second wave of the Great Migration by African Americans from the South to the North was larger, involving more than 5 million people, but it took place over decades, from 1940-1970. By 1940, 2.5 million people had moved out of the Plains states; of those, 200,000 moved to California. With their land barren and homes seized in foreclosure, many farm families were forced to leave. Migrants left farms in Oklahoma, Kansas, Texas, and New Mexico, but all were generally referred to as "Okies". The plight of Dust Bowl migrants became widely known from the novel The Grapes of Wrath by John Steinbeck.