You're also crazy to accept such insane lumpings of people. That would be like saying roughly 12 states in the middle of the US are all collectively developing a new accent. I don't think you realize how big some of the states out here are.
Some in the north has a curious accent, some in the middle have a rural one, too. There is no standard, though, and you have to split it on culture, not even on color, because it doesn't divide cultures. However, the most common is rather neutral. My theory is that this is because people migrated here from everywhere, especially in Los Angeles. NYC and the northeast in general ended up with nasty-sounding accents because many immigrants didn't speak English. However, Los Angeles ended up with a smooth, neutral, non-accent because everyone that already spoke English moved there and it merged in their children. Today you have second, third, and fourth generation people that grew up in an environment where there was no real local accent. That's how you end up with no accent, or a neutral one.