The book is like a rather long-winded and informal dictionary of the place names of California. If you don't speak Spanish or California Indian, and even if you do, you wouldn't be able to guess the reason why some places have their names. This book is the only source you can found that explains them.
Broken up into sections geographically, it, for instance, tells about the old Spanish ranchos and some of the transactions that occurred to place them where they are today - as cities, sections of a city that absorb them in part or in whole, open spaces absorbed by military installations, etc. It also tells about the old Spanish main roads that have been transformed both physically and name-wise.