For a book published before I was born, this is a very sympathetic and thorough account! I actually learned neat things from this book, such as the technical aspects - with diagrams - of how to make different arrows for different types of game. There is a chapter about the lone woman from San Nicolas island, about life before and during (and after) the Mission, about clothing and jewelry and trade. The back includes a multi-page bibliography.
I will mention that the book is a bit old, and was written with the late-20th century assumption that the Gabrieleño had been largely assimilated into the broader Mexican-American population of SoCal. Since it was published, there has been some community organizing of Gabrieleño descendants.