Lists, alphabetically by state and city, all campgrounds where overnight camping fees of $12 or less are charged. It provides its buyers with an opportunity to save significantly on their travel costs.
This book saved me some money, but my experiences were not always pleasant. Some sites were crowded. Neighbors were not always nice, quiet, or even civilized. Some were rude, territorial, suspicious, even paranoid. Not to mention their dogs. One site was closed, another was inaccessible in wet weather. But some of the primitive sites were good, such as the Kofa Wildlife Refuge on the Arizona desert. Joshua Tree Monument was interesting, but the campsites were too close together. On Mt. Shasta I had to go to 6500 ft. elevation to find privacy, but it was worth it.
Recommended to snowbirds and vagabonds, if there is an up-to-date edition available. It will point you to campsites that you might otherwise miss. But be warned: Saturday nights can get rowdy. Some of these sites are favorite party venues for locals. Free campgrounds are unsupervised, so you will be on your own.