National Geographic Guide to the National Parks of the United States, 5th Ed.

It is a beautiful book but as it says in the first paragraph, there are 5600 state parks, but the book only covers about 4 or 5 per state. Although that comes to over 400 state parks, its nowhere near the number that are available.
The descriptions of the parks they cover are great and they seem to hit all the main points.
The part that is irritating is that they don't provide a list of all the state parks so I couldn't even figure out what else there is to visit in a particular state. This forces me to go to the state web site to find out what else is in the state. I bought the book so I wouldn't have to spend hours on the computer going to individual states.
The book has been an aid to me in my travel planning, but much less than I expected.