This one is way easier than it sounds. Simply start up the game and find the nearest town (I'm new at the game, so I don't quite know yet how to navigate). Once you find a road sign, press the "Hand" icon and then go down the list, tapping each location until you've visited all of them for Arizona/Oregon, then repeat for the other state. For a fast travel to the other state, go to the bottom of the Road Sign and click the "Travel to *state*" button. This should take no more than a couple minutes at the most. The real trouble is first finding one Road Sign, but once you find one, you can easy travel to every location and get this achievement. Hopes this helps!