Boondocking at North Rim Grand Canyon?

I have a question for you guys, I am a corn belt flatlander from So. ILL, I don't get to boondock much as there are really no place around here to do it, I am not asking for your personal spots or nothing, but some day we are going to be doing more traveling out in the western parts of the country, how do you find and or know where you can camp on BLM or SF/NF lands.

I see all these pics of guys parked at remote lakes high in the mountains and I really want to find these places, and realize it can take some miles of rough roads to do so.

thanks Dar & Barb