I don't think I would specifically characterize it as "southern", though. I don't really think of the parts of Appalachia in western Pennsylvania, western Maryland, and even parts of West Virginia as being particularly "southern". But they are important sources of the mountain culture that has contributed a lot to the music that is called "old timey" by the people who live in that region and the rest of Appalachia. I know that parts of the south have contributed as well, such as the piedmont region of North Carolina, but it's not specifically "southern".