Pittsburgh, which seems to be the Galapagos Islands of American dialect.
“Pittsburgh is a special case,” Professor Labov said. “Generally, local dialects have been absorbed by larger regional ones. But Pittsburgh, though part of the Midland, has retained its own speech patterns. In fact, Pittsburgh does things no place else does, like pronouncing ‘ow’ as ‘ah’ and very often dropping the ‘l’ when it comes at the end of a word.” (Radial, for example, winds up sounding like radio.)
Julie Schoonover, the barkeeper from Corning, had described the dialect of the Steel City (a k a Pixburgh) more succinctly: “If you want to hear some freaky talk, go to Pittsburgh,” she told me. “It’s all ‘yinz goin’ dahntahn’ down there.”
And later expanded on in The Pittsburgh Post-Gazette.