I bought the Boondocking in Southern Utah guide from Frugal-RV-Travel. I had read excellent reviews about the book, and I have to agree that the book is excellent. They list a bunch of boondocking sites, with directions and GPS coordinates. The cost was $17.
They produce six different boondocking guides, on New Mexico, Southern Utah, Southern Texas, Arizona, California Sierras and Coast, and California Desert and Eastern Sierra.
The guide comes as a pdf file. I loaded it onto my computer, iPad and iPhone. I put it in the Kindle app on the iPhone and iPad, but the iBook app works also. If I am driving, my wife will be the researcher / navigator, and she likes paper, so I printed out a double-sided copy and put in a report binder. The first version of the book I got in 2017 was the 2013 edition, and it was 140 pages long. They revised the book in 2018, and they send me a copy of the new edition. It is amazing that they sent me the updated edition for free! The new version is 166 pages.
The GPS coordinates are hot linked. If you click on the GPS coordinates it opens up in Google Maps, either on the computer or on the phone. Very cool!
I highly recommend these guides.
Using the Boondocking in Southern Utah guide, I found the best campsite I have ever had, in Valley of the Gods in Southern Utah. The campsite on BLM land was free, so I definitely consider the $17 for purchasing the book money well spent.