Wondering what the best "Yii way" to do this would be

I need to add a feature to a site where users can select the US state(s) and region(s) within those states that they provide professional services in.

The client wants the user to first pick a state, and then be able to select multiple pre-determined regions within that state.

For example, they could first select California (maybe from a drop-down). Then, they are shown the regions in California (Northern California, Bay Area, Southern California, etc), and they can pick which of those regions that they provide service (maybe using checkboxes or multi-select list). Then, they can pick Texas, select the regions in Texas, and so on with as many states/regions as they want.

Any tips for the most efficient/user-friendly way to go about this?

Thanks.