This book is outstanding. I'm an avid canyoneer and these books got me started. Many think they're too good. I follow the canyoneering boards and people consistently complain that Kelsey gives away too much information and allows, "just anyone who buys the book" to get in the deepest, darkets canyons. The land managers down right hate these books because people get into trouble. I think a good guidebook tells you about an area and it's up to the individual to be responsible and not exceed their abilities.
Aside from the extermely thorough and detailed area information, Kelsey takes pains to explain the history of the area and to prepare you for what you need to do spend time in these strange lands. I have hundreds of guidebooks from around the world and none of them comes close to Kelsey's in these areas. They are a treat to read.
There are a few quirky things about Kelsey's work. He lists everthing in metric. I agree this makes perfect sense from a technical (the rest of the world is metric and it makes much more sense) point of view but still have to do a poor job of converting everything back to miles in my head. It would be better to list miles in brackets after the kilometers. Kelsey is also (apparently) very fit because his hiking times are impressively rapid. I usually add 50% to his times to get a realistic estimate of how long it will take me.
All in all, I couldn't recommend Kelsey's books more. He is an extremely hard working, dedicated author. His works are jewels for this area and will long be recognized as not only the geographical authority but also the historical authority in this wonderful part of the world. Buy everything he writes.