So the Joads headed to Cali why?

"The country’s biggest agricultural engine, California's sprawling Central Valley, is being battered by the recession like farmland most everywhere. But in an unlucky strike of nature, the downturn is being deepened by a severe drought that threatens to drive up joblessness, increase food prices and cripple farms and towns.
Across the valley, towns are already seeing some of the worst unemployment in the country, with rates three and four times the national average, as well as reported increases in all manner of social ills: drug use, excessive drinking and rises in hunger and domestic violence."
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