I created a map of the So Cal desert for off-roading. It was initially of the Ocotillo Wells and Anza-Borrego desert area. I recently expanded the coverage area to include all of San Diego and Imperial counties and the southern part of Riverside county. I created the majority of the data myself and it is the most accurate and up to date map available. 3,700 miles of OHV trails and 2,700 miles of street legal trails.
It's available for Garmin and Lowrance GPS receivers. The Garmin version also works on PC and Mac which is useful for trip planning.
Garmin allows more customization and control of the map than Lowrance. Trails on the Garmin version are color coded to indicate if they're OHV or street legal only. The Lowrance version has all of the same trails but doesn't have the high-res custom graphics or a topo version.
Check out the website for more info or let me know if you have any questions.