Where is the dividing line between the Appalachian Mountains and the Allegheny Mountains?

Answer 1

Here is an awesome that will hopefully help you:

Major fault at the dividing line between the Allegheny Plateau and the true Appalachian Mountains Williamsport, Pennsylvania The rock layers on the left are metamorphic, while the rock layers on the right are sedimentary.

http://upload.wikimedia.org/wikipedia/en/f/fa/Junction_fault_0112.jpg