My initial surprise, upon receiving this book, came from reading the back cover, and noting the observatories not included.
The Lick Observatory has what once was the world's largest telescope, the 36 inch refractor. It also has a 36 inch reflector that was the first major reflector using a metal coating on glass, the model for all of the large telescopes of today. Decades later, the 3 m Shane telescope became the second largest in the world for a while. Not included.
The Mt Wilson Observatory has a 60 inch telescope that was the largest in the world until its 100 inch neighbor, the Hooker telescope, saw first light. The Hooker was the largest in the world for three decades until the 200 inch was completed on Palomar Mountain. Mt Wilson also has three major solar telescopes, and was once the leading solar observatory in the world. Not included. (Which is especially odd given that in his preface coauthor Strom mentions how he was influenced by a trip to Mt Wilson as a young teen.)
The Big Bear Solar Observatory is building what will probably be the largest aperture solar telescope in the world when it is completed. (Although much larger solar telescopes are planned elsewhere.) Not included. (This is less surprising, given that Big Bear has a lower profile than many observatories, and is currently closed to the public due to construction.)
One might think that the authors don't consider California part of the southwest, a not uncommon view in neighboring states. Yet there is Palomar! (Maybe too important to leave out?) Facing the introduction is a map of the southwest that includes much of California. Mt Wilson and Big Bear would fall cleanly on the map. It looks to me like Lick would be right at an edge. Not the choices I would have made, but it's not my book.
The next mystery was about authorship. The book is credited to "Douglas Isbell and Stephan E. Strom". But the preface is by Strom, and the "About the Authors" page lists Strom first, with about twice the lines devoted to Isbell. Yet it appears Isbell did the heavy lifting.
The general structure is that for each observatory there is a few page history, followed by information on visiting the observatory, followed by an interview with someone associated with the observatory. This all appears to be Isbell's work. Then there is a few page "Science Highlight" about something related to work done at the observatory, apparently by Strom. (The interview and science highlight are omitted from the final entry covering Mount Graham.)
The histories are serviceable, but not a lot more than you can find at most of the observatories' websites. Likewise the information on visiting can be found on line (and should be current). The interviews are not all that interesting. And the science highlights won't be greatly illuminating to most of the people who would be drawn to a book like this in the first place.
Not a bad book, exactly, but not a very useful one, either. You can probably do better looking up observatories on line.