Very cool Eric,that appears to be some Borax Lake Gray?I grabbed a piece of the Davis Creek yesterday from the Ranch....I need to take some pics of it.Folks dont realize on here that it only comes from two places that I know of.....Borax Lake(by you)and Davis Creek.That does appear to be a fragment of a pestle.I was told.....and given the fact I have found "piles",of those...and none fit together....that when a pestle would break,they would use the fragments as heating rocks.They would put those rocks in the fire/coals,then with a forked stick would put them in a basket of acorn mush,or cattail tuber mush etc,and stir....thats how they cooked in baskets