In 1930 and during the subsequent decade, 2.5 million migrant workers left the Plains states due to the destruction caused by the so-called Dust Bowl. Between 200,000 and 1.3 million of these migrant workers moved to California, where they became seasonal farm laborers.
Approximately 40 percent of the migrant workers who migrated to California ended up picking cotton and grapes in the state's central San Joaquin Valley, where they displaced hundreds of thousands of migrant workers from Mexico. Migrant workers in the San Joaquin Valley earned 75 cents to $1.25 per day, but often had to return much of their earnings to the corporate-owned farms on which they worked in order to rent a shack to sleep in and to buy food from the company store.
Many of the migrant workers had owned their own small farms in the Plains states and hoped to save enough money to start their own farms in California. However, as many as one-third of migrant workers in 1930 and the subsequent decade were white-collar workers and professionals who had lost their jobs due to the Great Depression and moved west to seek a better life.
Extreme drought conditions brought on the Dust Bowl of the 1930s, in which topsoil in Oklahoma, north Texas and neighboring states blew away in large quantities, destroying the formerly productive agriculture of the region.