Religious Adherents: Concentrated in Central US

I was perusing various maps of data. I visited a favorite website of mine that has a great set of maps of religions in the United States. One stood out to me just now. It is a map of religious adherents:

Map of Religious Adherents as a percentage of all residents, 2000

 

The pattern of the highest concentrations of religious adherents doesn’t follow the pattern one would suspect. It doesn’t follow the Bible Belt (the Bible Belt may get the most attention, but maybe its not deserved). It doesn’t split between the North and South or between the East and West.

It is mostly situated in the central core of the country. Besides the Mormons, it sticks close to the 100th Meridian and the Great Plains.

I was wondering what religious patterns it does follow. The only two maps that show some similarity are those of the Methodists and Catholics, but I don’t know why that might be or if it is significant at all. It’s very intriguing, whatever its cause.