* It's a misspelling. It might be a variation of a real word or phrase, like "Alma Mater" which means "nourishing mother" and refers to a university or school.
* It's a regional or dialectal expression. Perhaps it's used in a specific community or location.
* It's a made-up phrase. Someone could have invented it for a particular purpose, like a book title or a brand name.
To find out the meaning of "Alta Mata," you need more context.
* Where did you encounter this phrase? Was it in a book, a song, a conversation, or somewhere else?
* What is the surrounding text or context? This can provide clues to the meaning.
Once you have more information, it might be easier to figure out what "Alta Mata" means.