Linguist, Rick Aschmann, has wonderfully detailed maps of the various dialects of English used in North America. It includes lots of audio samples of speech, and is excellently annotated.
Given that dialects are great integrators of cultural history, including the history of immigration to the different regions, this may well be an excellent resource for this cycle’s work on U.S. immigration.
The r-dropping areas in the Lowland South … could be described as “Classical Southern”. This is the accent that Scarlett O’Hara is attempting to imitate in this clip from Gone with the Wind. This area represents the heart of the old plantation system, as can be seen on the map mentioned above. However, this feature seems to only occur in older settled areas, and does not occur in western areas on the Mississippi River or farther west that were settled after about 1825.
— from American English Dialects by Aschmann, (2010).