San Bernardino National Forest- so many great spots! doesn’t feel so arid as the rest of SoCal does which is amazing. I went to Deep Creek Hot Springs on a backpacking trip. That hike down to the springs was extremely hard and I wouldn’t actually recommend it, but driving through that area in general is so beautiful.
San Luis Opisbo- TV Tower Road is a little known free dispersed camping road that goes up a mountain. Car camping is perfect car because it does get windy overnight in a tent. Over 3h from LA but if you’re on a trip north its so worth it
Joshua Tree- but go to 29 Palms for cheaper camp sites. I’ve found great deals on HipCamp on ppls property. I love hiking and climbing the rocks in the national :))