I know this is low-tech, but there is a series of road atlas's available for the western US, by Benchmark Maps.
Available in the chain type book stores for about $20 each .
The maps get down to dirt roads, and identify 4 wheel drive only roads, and also identify local sites of interest, that you can look up on the internet .
The maps are available for California, Arizona, New Mexico, Colorado, Utah, Nevada, Oregon and Washington state .
You can plan your route ahead of time with pretty good accuracy with these, then use your GPS for fine tuning your route instructions .