ATV recreation areas are available on a variety of public lands. You can reach out to your local land management agency to learn about riding areas and restrictions. You can also ride your ATV on your private property or someoneelse's private property with permission. You can get more information on State Vehicular Recreation areas on the California State Parks website. You can also view Bureau of Land Management Recreation Areas and National Forest Recreation Areas.
Check out these Mount Wilson, CA ATV/OHV resources:
