The correct answer is that many farmers left their farms for California due to the effects of the Dust Bowl.
The phenomenon of the 1930s known as the Dust Bowl was one of the worst ecological disasters of the 20th century. The drought affected the plains and prairies that extend from the Gulf of Mexico to Canada. The drought lasted at least between 1932 and 1939, and was preceded by a long period of above average rainfall. The dust bowl effect was caused by persistent drought conditions, favored by years of soil management practices that left it susceptible to the action of wind forces. The soil, stripped of moisture, was lifted by the wind in great clouds of dust and sand so thick they hid the sun. These days they received the denomination of "black blizzards" or "black wind". The Dust Bowl multiplied the effects of the Great Depression in the region and caused the largest population displacement in a short space of time in the history of the United States. Three million people left their farms during the 1930s, and more than half a million emigrated to other states, especially to the west.