I think you're asking for regions in the US, not cities, where you can meet lots of people, so as to demonstrate diversity.

Well, there are plenty of black people in the deep South. There are plenty of latino ranchers in the Southwest. There are some pockets of even non-English speaking folks in Louisiana and the Chesapeake.

But that's not diversity, that's just a different homogeneity. Although I can certainly attest to the fact that, going to school in New Orleans, life does feel a bit different being in the minority locally.

Cities, particularly coastal cities, have been melting pots, world-wide, for a long time. Since long before Columbus landed in the Americas.

If, by diversity, you want to meet a lot of people from different walks of life, you pretty much have to go to cities.

Now, is San Francisco the ultimate sink to which sources of diversity converge? Probably not. But I've been in every hemisphere and most major US cities, and San Francisco is pretty solid. You just have to get outside the bubble a little.

You want insane levels of homogeneity? Try Tokyo.