Find a local Jeep owner club and tag along. That’s the best way to learn. Check out the CA section on here; ask your Jeep dealer, etc.
When you approach a group of Jeepers coordinating an outing, make sure to let others know whether your Jeep is stock or not, whether it has a lift/lockers/33+ tires, and your level of expertise. You don’t want to go with a hard core group and find yourself way over your head.
Not that I’d recommend this to anyone new to off-roading, but a few years ago I went to Hollister Hills Off Road State Park, near San Juan Bautista, CA: it is a hoot!!! You definitely want to go with someone experienced.
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