This review is being written simultaneously from the point-of-view of someone who attempted to read the book for fun and from the point-of-view of someone who used the book while hiking on the John Muir Trail.
I picked this book up at the suggestion of my backpacking partner several months before we embarked on our John Muir Trail journey. I was very excited about the trip and impassioned to learn as much as I could before the start. I think I lasted 5 pages - I am not kidding. This book is so dry and so boring. Think back to your last backpacking trip... If you wrote a book about all the minuscule plant and animal life, views, and geography that you encountered across your multiple, day long hikes, would you want to read that? No. I wouldn't want to, and I wouldn't want anyone else to (looking at my pictures is of course a different story...)
HOWEVER, if you are currently on the trail being described or taking a break beside the trail while your partner does his business, then this kind of information is interesting. Or, if the sun is setting and you need to find the nearest acceptable campsite, then this information is rather helpful. Or, if you lost your water filter and need to know if you'll die if you drink from the nearest stream, then this information is really helpful! (that didn't happen but you get the idea).
I carried this book with me for the full 215ish miles of the John Muir Trail in August of 2017. My partner and I did the hike in a brutal 11 days. I used this book every single day to review campsite information, elevation profiles, and prepare myself for the days ahead. The text was no more interesting or engaging but at least it was relevant. It gave me fun facts to tell my backpacking partner along the way, too. If I had to do it again, I would rip out all of the relevant charts and maps and leave the rest of the book behind.
So, three starts because of its utility. No more because it is boring.