Mexican/Southwest US stone tool. I think it might be for cooking?
I had originally posted this to Reddit but the mods removed it and suggested I take it to a rock and minerals subreddit.... which was infuriating. Anyways, this came in a collection of other Mexican arts and pottery. I have not found anything exactly like it online. I actually have a pair of them. I thought it might be for tortillas but it seems small. It's abou 4" across. Any help is appreciated.
You can see on the rim the different wear patterns where maybe they were grinding too much at the side. If that's not a hand mill I'm not a Stone Mason.
I was picturing something more like a mortar and pestle but this makes more sense! It's just like a mill you'd find in, well, a windmill, but smaller and hand operated.