The Southern story has, at its core, a secret that should never have been revealed. That secret is slavery. (Sometimes, the secret seems to be adultery or incest or brutality, but it all goes back to slavery.)
The hidden core of the New England story is the haunting memory of Europe, filled with violence and hatred and the certain knowledge that nothing will ever change here.
The Western story – the genre, yes, but also Hammet and Chandler and Angels In America – hides the terrible knowledge that, in the end, you will stand alone.
In the Midwestern story, we learn that the City is not the bright and shining wonder it seemed when we arrived (for the Midwestern story — Sister Carrie or The Wizard of Oz, Horatio Alger or First Foundation — always begins with arrival), and that in its very corruptness we see our reflection.
Thanks to the Readercon panel on “New England As The Home of Unheimlich” for the explaining the Southern and New England stories. They aren’t responsible for the others.