Per the Associated Press, these were the U.S. cities with the highest unemployment in May, 2012:

Yuma, AZ 28.9
El Centro, CA 26.8
Yuba City, CA 17.9
Merced, CA 17.3
Modesto, CA 15.6
Fresno, CA 14.9
Hanford-Corcoran, CA 14.8
Visalia-Porterville, CA 14.7
Stockton, CA 14.5
Madera-Chowchilla, CA 14.3

Whatever could all those have in common?

If you aren't familiar with this corner of the world, all are agricultural areas, and most are in California's Central Valley. And, all those cities are home to large illegal alien populations engaged in various agricultural fields. (There are other factors such as the Delta Smelt, but those other factors' impact would be reduced if not for the very large numbers of illegal aliens in those areas.)

The way to reduce those numbers is to encourage able-bodied, unemployed Americans to work in the fields, even if only temporarily.

The alternative - one favored by self-styled liberals like Stephen Colbert - is to import a foreign serf labor class who'll do jobs Americans could be doing. In addition to increasing the costs of unemployment (fiscal and social), that also lets foreign governments off the hook: they can send people to the U.S. instead of taking care of their own people.