What is the meaning of grinding slicks / metates at shamanic sites in the American Southwest? Nobody grinds seeds for lunch in a temple high on a windy mountaintop. There must be some other explanation. If you have expertise in this topic, please join the discussion!
Here’s a video of the topic in question. Please watch before you answer.
THE ANCIENT SOUTHWEST 
You are correct. For the kumeyaay the kuseyaay wouls grind up the ceremonial herbs needed for whatever they were doing. I do believe they would eat there though, because they lived there. They believed the creator gave them all things so i don’t think they saw making food than as we do now.