Are you considering the practice of magic itself be different in the regions of the country, rather than just the elements themselves? I don't mind going in more depth, granted we can keep track of everything. If you're into that, we could probably map out the general areas of the US, be it north/south/east/west? I'm a sucker for chants, magic circles, probably alchemy (not just magic circles but with herbs and natural stuff) and possibly potion making or voodoo? For the south perhaps.