In order to find the best camp spots you must get away from the crowds & head for the hills, the rural spots, the back roads. You can enjoy primitive style wilderness camping without having to lug your 50 pound backpack 10 miles up hill. With a decent forest map, there opens up plenty of new options. Dirt roads to explore, waterfalls to hike to, meadows to camp next to, streams to fish in. If you have an SUV & want seclusion, there should be no reason why you have to stay in those noisy highway campgrounds.
Make sure you have a valid campfire permit & you are free to roam. The Southern California Forest has stringent fire restrictions, but you can still find back roads camping if you want to look, although campfires are generally restricted to developed campgrounds only. Call the local ranger for assistance.
BLM land (Bureau of Land Management) is usually mixed with private property & sometimes bordering National Forest or State Park lands. Make sure you pay attention to signage & respect the no trespassing laws. BLM land can be a great find for some small unknown campgrounds with little or no fees.