I stumbled upon this fascinating site recently - muturzikin.com - the webmaster of which draws linguistic maps displaying different languages and dialects across continents. I always knew that there were plenty of different American English dialects across our country, but I didn't expect quite so much detail on a map of the USA. Click on the image below to see the full sized version - be warned, however, the full sized .png is huge (3567×1878, 301Kb), so you might want to open it and then right click -> save it to your computer and view it that way.
So here, it is, a map of indigenous languages, dialects and accents in the USA:
It's amazing to see just how many Native American languages and dialects remain around the nation. This must have taken a long while to put together, but it was clearly well worth it!