Dust Bowls (where, when, how)
Go to these web sites to find out about the Dust Bowl:
                    http://drylands.nasm.edu:1995/dust.html
                    http://www.pbs.org/wgbh/amex/dustbowl/
                    http://www.discovery.com/area/history/dustbowl/dustbowlopener.html