I grew up in the foothills of the Angeles National Forest here in California. In my teenage years, I would often go up and camp wherever I damn well pleased. At sixteen, I was camped out in a clearing deep in a valley. I had walked there (they usually find you by spotting your car) and used a deer trail to get to my spot. About an hour or so after setting up my tent, I hear thrashing through some bushes. My first thought is bear, but it turns out to be a park ranger. His response was great, at first he seemed all bulstery with authority, and pretty upset.
As he realized how young I was, he calmed down and was more interested in how I had made it there, was astounded I had walked from my home (only about 8 miles away, and only 3000 feet down) When I explained that I hated camping with a bunch of drunk idiots in cars and RVs, he laughed. He made me break down my tent and offered me the option of a ride to an official campsite with a fee waiver or home, I chose home.
On the way back up the hill on a trail he didn't even know was there, I buttered him up by asking him about his job, neat things I might not have seen in the forest (I wound up telling him some places he didn't know about) and when we got to his truck, he gave me a phone number and told me how to get a backwoods permit, which would allow me to camp anywhere I wanted in state and national parks in California.
They don't advertise it, and you have to know the terminology to ask for it, and I agree with this. If they allowed everybody to go backwoods, then all the drunk idiots who can't clean their site, even with dumpsters placed between every other campsite would be out there leaving cases of beer cans, burning down the woods and leaving turd monuments at every clearing.
I do LOTS of stealth and guerrilla camping, and have been busted once recently, camped out in a forest behind a vineyard. Only reason I got busted was because it was POURING out, and the vineyard was flooded so I stayed in the tent until 10 am. My thoughts were, "Forget it, they are going to have to boat me out of here. . ."