There’s books out there that have documented some of the best burger joints and regional varieties across the US. There’s a lot of them and it’s pretty surprising how diverse it can be based on the preparation method and ingredients/toppings used. That would be a pretty killer road trip.
There is actually a cook book called 'Hamburger America' by George Motz. It showcases all sorts of variations across the states.
He's one of the cool dudes on First We Feast(Hot Ones channel) with as one of their shows.
A hamburger is the first thing that comes to mind when thinking about a quintessential American dish. It also has lots of regional varieties.
I recommend watching Burger Scholar Sessions with George Motz on the First we Feast YouTube channel. He's actually written a book as well about all the different regional burgers in America.