The dust bowl is a hard topic to comprehend. PBS has done a wonderful job collecting and organizing material for this event in American history. It can be found at http://www.pbs.org/wgbh/amex/dustbowl/index.html
This topic can be as short as you would like by choosing to only part of the activity or it can take up to three hours if you choose to do all three parts.
I tend to use 90 minutes for the research and question sheet, 60 minutes for the video, and 30 minutes for discussion and the journal activity.
This activity includes the question sheet, answer key, journal sheet, and link to the video.