Midwestern farmers felt the Depression particularly hard because of over production of crops leading to increasingly cheap prices (FDR tried to mitigate this with subsidies); mechanization of the Agriculture and the growing agribusiness, as small time farmers didn't have the resources or money to compete with the big, mechanized farms; and most importantly, the dust bowl, which caused hundred of farms throughout the Midwest to fail.

I don't know of any government effort to direct Midwestern farmers to California, but I know that many destitute farmers headed west because of the promise of fertile lands (as their own farms had just dried up), and the potential to grow a diverse range of crops which would be difficult for large farm businesses to monopolize on, versus wheat or corn.