What year did the people leave the dust bowl and how many people left like the people and the farmers exactly how many of them?

In the 1930s, farmers from the Midwestern Dust Bowl states, especially Oklahoma and Arkansas, began to move to California. As well as  250,000 arrived by 1940, including a third which moved into the San Joaquin Valley. That at that time had a population of 540,000 in 1930. During the 1930s, some 2.5 million people left the Plains states

People left the Dust Bowl by 1940, 2.5 million people had left the Plains states: of those, 200,000 moved to California. 40% of the population dropped with 1,642 small farmers and their families pulling up stakes.