I saw your posting my grandmother Josephine Frates grew-up in the Diablo Valley. She eventually married Antone Borges and they settled in Hayward. My grandfather came from the Azores and I think that my great grandparents came from either Portugal or the Azores. I have seen your great great grandfathers name on a list of land in Contra Costa that had his name on it. I suspect but are not sure whether your great grandfather might be my grandmothers father. The description of the land parcel says it starts from the foot of Mt.Diablo and according to what I was told by my aunt my great grandparent's land did too.