The Dust Bowl migrants were just one of many groups who have worked the farms of California in the past two centuries, usually for low pay:
American Indians worked on Spanish mission farms near the coast in the late 1700s. Indians also worked the vast cattle ranches that dominated California under Mexican rule in the early 19th century, and the wheat farms that followed the Gold Rush.
Chinese became the main group of farmworkers by the 1870s, after helping build the state's railroads. They played a large role in establishing fruit and other specialty crops but faded away about 1900, largely because of anti-Chinese sentiment.
Japanese immigrants arrived about 1900 and quickly became a major force. Many worked around legal restrictions on land ownership to become farmers themselves. Some lost their land during World War I, and they ran into immigration restrictions in the 1920s.
A smaller wave of immigrants from India worked the fields from roughly 1910 to 1920.
Mexicans became a large part of the work force around World War I, which brought a labor shortage. Their numbers fell off in the 1930s as the Depression created a surplus of workers, including the Dust Bowl refugees.
Filipino workers were prominent as well in the 1920s, but they also faced racist barriers.
Mexicans became the main labor force during World War II, when the Bracero program was created to ease a labor shortage. That program is long gone, but Mexico remains the main labor source. Meanwhile, descendants of earlier farmworkers from that country have moved up in status in the state.