There are BLM field offices -- just call them on the phone. They are very friendly.
Also try the national forest ranger stations. You can download their Motor Vehicle Use Maps. The Avenza app should show your location on your phone.
When you get more comfortable with boondocking, try using Google Earth to fly along forest roads. When you come to a fire ring, you have probably found a campsite.
Boondocking is a lot more work than campground camping, and very time consuming. If you like isolation, it's worth the trouble.
