The steps below will allow you to restrict the US States that a user can pick from when checking out in Ubercart. This was useful for me when a client needed to restrict shipping bottles of wine to various states that don't allow that sort of thing.

Source: http://www.ubercart.org/forum/support/11620/limit_us_states_list_48_cont...

In filesystem:
Go to .../all/modules/ubercart/store/countries and modify the "united_states_840_1.cif file. Backup this file since you may need it later. Open the file with a text editor and delete all the lines that you don't want to appear in the States list. Save the file with the original name.

In Drupal:
Go to "Administr/Store Administration/Configuration/Country Settings" and select the Edit tab. If you already have the United States there, remove it. Then, select from the list "united_states_840_1.cif" and press the Import button. You can now check the list of states in your Checkout form.