Could it be that there are no jobs for them to take? They aren't exactly collage graduates, and Mexicans take every low paying job. It's not a good situation for anyone.
This is what happens when the liberal social system collapses, you end up with millions of uneducated people who come from generations raised by the welfare system. What can be done with them? Perhaps spreading them out to other cities is the only thing that can be done to lighten the burden. Good luck trying to move them to colder states.