I'm a bit of a mapping / navigation junkie, currently I run a android tablet and import google earth imagery as detailed here: http://socalbajas.yuku.com/topic/2677/Android-based-offline-GPS-mapping
This is nice, and provides an overview of the terrain, but the storage requirements are such that you can only really get a small amount of the areas you may drive in on the system, and the technical requirements of the operator can be a little much. Furthermore, you are still reliant on your own sense of direction, as there is no kind of navigation off road.. until now..
I have found a solution that I think is the best option for turn-by-turn offroad navigation. There is a mapping provider / service called "OpenStreetMap" which is essentially the wikipedia of mapping, meaning that anyone can add to, or edit the map as they see fit. The great part is, once someone has done the mapping, its done forever and available for everyone.
So, I have started by tracing over some of the larger dirt roads in the Stoddard Wells OHV area. I tag them as "Dirt Tracks" and assign them a terrain quality of "High Clearance" or "Offroad vehicles only". These keep the routes off of the normal automobile turn-by-turn, but should allow us to tailor baja navigation that actually prefers these types of routes. All the editing is done in-browser, and is pretty easy, and even gets addicting after awhile. Here is a screenshot of some of my mapping:
Here I have added many of the dirt roads in the area and even some of the common camping areas.
The mapping itself is step 1. Step 2. is going to be setting up a device to read the maps in car. Apparently, there is a pretty simple conversion you can do and get these maps displayed in Garmin GPS devices. The most straightforward is to use an android or iPhone device and install an App that uses the OpenStreetMap standard. I'm planning on using a full double-din android head unit in my build, which should provide a pretty nice navigation experience. http://forum.xda-developers.com/wiki/Newsmy_CarPad_NU3001
Stay tuned here for updates. In the mean time head over to openstreetmap.org setup a user account, and start mapping your favorite off-roading areas. In the end we should have a pretty bad-ass option for dirt road navigation.