It is principally a listing of the handwritten mission records for Southern Baja California between the years of 1700-1900. The records include baptisms, marriages, and funerals. There are few records from the first 100 years, as immigration to Baja and Alta California was not permitted by the Spanish government. Still, there were a few exceptions, mission soldiers' families and such. After 1824, the Mexican government permitted immigration, and the number of citizens grew rapidly. There are also some interviews of live citizens of Baja Sur who know their ancestry way back on the peninsula. There is a bit of history of the early days of the peninsula. That part and the interviews are bilingual in Spanish and English. I have found the book in the state archives for Baja California Sur in La Paz, Stanford University, and UC Berkeley.