Me and a friend were talking about this, and realize that the civil war and wild west and escapes from slavery lend themselves more to epics than to all the other things we hear in most "Americana" material, but we don't seem to really have any long folk epics.
The Odyssey was not a song or musical form. It was an epic poem and was recited in a form closer to theater.
The Epic tales exist in American tradition in the form of Tall Tales, some of which are very long with numerous side stories.