A hyperbole is an over-exaggeration. In this phrase, it is highly unlikely that the little city in Georgia has been sleeping for "forty thousand years" especially considering that the United States is only 242 years old. If personification were an option, it would also be a great choice. Personification is giving non-human thing human-like traits. In this phrase, the city (non-human) is being given a human trait (dozing).
The other options: an allusion is a reference to another piece of literature or other published work. A flashback is an interruption that tells about something that has already happened. Rhyme is a group of words that sound similar (bone, cone, phone).
