I created an online map to locate public lands in San Diego, Imperial and Riverside Counties. It brings all publicly accessible lands together in one map to make them easier to find. Many of the areas aren't documented or mapped anywhere else on the Internet.
Select Motor Vehicles from the Filter menu to only see the areas that permit off-roading:
There’s an information page for each location with a description, permitted activities, trail maps, pictures, regulations and links to resources for the area.