is the most scenic!

As for navigation, is that not something that comes with your cellphone (if you have one)? Not being much of an International traveller, I really don't know much about cell phone compatibility in the US for your phone and carrier, however, you might be able to have a temporary upgrade of services.

Might also be possible to rent a cellphone here in the US, that has a navigation as a feature.

Also, will you be travelling with a laptop or pad? If so, look to free WiFi hot-spots to link to Google Maps. Also, broadband devices can be rented to link a laptop to a cell network for Internet access.

Many possibilities.

Jim