State Department of Transportation (DOT) maps are generally free (I expect Jennifer will jump in with the the appropriate URLs as soon as she gets to work), and provide pretty good overview down to the state highway level, sometimes better. For finer detail, DeLorme publishes atlases for each state. I don't know if they include all the county and Forest Service roads; if not, you'll want to go to detailed topographic maps. I'd recommend you get one of the computerized topo packages and plan things out on your nice, big monitor before you leave; the alternative is several large file cabinets full of hard copy topographic maps.
There's a lot of land out there. You do realize, don't you, that California alone is larger than all of Germany?