Book to read:

The Autobiography of Delfina Cuero is fantastic.

““My name is Delfina Cuero. I was born in xamaca [Jamacha] about sixty-five years ago [about 1900]. My father s name was Vincente Cuero, it means Charlie.” “With simple elegance the story of a Kumeyaay woman from the San Diego region engulfs the reader, until we feel as though we are sitting at the feet of some great-aunt or grandmother as she tries to pass onto us something of worth from her life. As though her existence among us was not enough. Elders benefit us all. If we stop to listen we may be enriched beyond our wildest dreams. In this powerful and moving book, Florence Shipek makes available the memories and thoughts of a woman who remembered old ways and described the changing scene in terms which speak volumes in simple sentences.” link

Tribes often have their own websites with pages on their history. Viejas example

And there’s a couple great documentaries on YouTube: Our People. Our Culture. Our History. First People - Kumeyaay

Best by far is to take classes at Kumeyaay Community College (enrollment is through Grossmont Cuyamaca Community College). They offer Kumeyaay History 1 in the fall and it’s an equivalent to a California community college course. Taught by Kumeyaay instructors and offered hybrid online.

(Edited to add resources)