Percentage of population that view scripture as the
Word of God literally true word for word.
Good news for Okies - we aren't the buckle after all! If the data from the Pew Forum's new Religious Landscape Survey are to be trusted (and I'm none too skeptical for once) that dubious distinction goes to to the Old South, both geographically and in terms of raw data.
Note that if you mentally block out the mustard-coloured states, you still get a contiguous belt centered upon Dixie, but aligned roughly east-to-west. That would be, I suppose, the traditional (fuzzy) conception of the proverbial belt. It is this inner-belt which votes most reliably in favor of the GOP, and which borders upon such key swing states as Florida, Ohio, Missouri, and Colorado, where a slim majority of citizens have not yet drunk the Kool-Aid.