The "melting pot" concept was a late 1800's, early 1900's description of the assimilation of non-Americans into the US. That era of immigrants largely clung onto many of their ethnic traditions (forming Little Italys, Chinatowns, Ancient Order of Hibernian groups, etc.), but almost all of them insisted that their children learn and speak English and conform to the dominant Anglo culture. In fact, most of these immigrant groups eventually moved up in society and moved out from the inner cities to the live the American dream out in the suburbs. As a practical matter, the melting pot concept no longer exists as it did back then. Today's immigrants are less likely to force their kids to speak English and they cling a little more to their homeland cultures. The US is now more like a stew pot -- individual immigrant groups maintain much of their own identity and form, but melt down a bit at the edges to add flavor to the underlying, (and still) dominant Anglo culture.
The melting pot does not exist as a concept in terms of regional differences among English speaking groups within the US. There can be huge differences in slang, food, belief systems, etc. within the US. So the food, slang and belief systems among Georgians can be vastly different from that of a New Englander. After the mass migrations of people from state to state after WW2, those regional differences have been growing fewer and fewer, but it's not really what Americans mean by the melting pot concept.