The dust bowl’s black dust spread through the plain states. When the storms showed no sign of letting up, many people abandoned their land. In all, 1/4 of the population left, packing everything they own. In the rural area outside Boise City, Oklahoma, the population dropped 40%! The dust bowl exodus was the largest migration in american history. By 1940, 2.5 million people have moved to the plain states; of those, 20,000 moved to California.