ACA and Google are starting points, but I wouldn't ever use those for my final route (which naturally changes on the road, but that's another story entirely). Since you've got some time, consider ordering relevant paper maps of the approximate route you get from other resources. National Forest Service maps are cheap and great and they are very useful in the west. They give details like if the roads were paved when the map was made, as well as the date the map was made. Even AAA maps are decent. Basically, look for the smallest roads and use those. If you aren't happy doing some gravel/dirt, then you'll need to make the effort to confirm pavement. If you don't want to go uphill, then you're back to the ACA maps, since they prioritize flatness (at the cost of increased traffic counts).