Selected enum based on selected value in combobox

I want to display a list of values in one combobox and based what gets selected fill values in another combobox.  So for instance i have these enums:

    public enum Region
    {
        Midwest,
        West
    };
    public enum Midwest
    {
        IA,
        WI,
        MN,
        IL
    };
    public enum West
    {
        CA,
        WA,
        OR
    }

I can bind Region values as the itemssource for a combobox no problem and get the selecteditem value in my viewmodel with no issue but I run into issues trying to create a property that will hold the values for either Midwest or West.  There's not really an enum base class that would reference both West and Midwest is there?  Maybe enums aren't the best way to acheive this.  How would you implement this?  I was thinking I would create a States property that I would then bind to the itemssource of my second combobox.