How did they form? What are their specific traits? Stereotypes (even untrue, if marked as such)?
If cultural differences coincide with geography, please mention in, too.
In the questions about weird things people from different continents do somebody pointed out, that Europeans have little knowledge of this, so please fix my ignorance.
The cultural regions are New England, the Mid-Atlantic, the South, the Midwest, the Mountain West and the Pacific.
Politically the South and Midwest are conservative. New England, Pacific, and Mountain regions are liberal. The Mid-Atlantic is a mix.
Cultural differences are largely based on popular religions or lack of religion.
That’s about it, Americans are pretty much all the same no matter what state or region you are from.