This is a mortar and pestle that was not part of the milling depression. This was used to make acorn mush. First the women would get acorns and crack open the shell to get the nut. Next they would use the mortar and pestle to grind the nut up into powder. The next thing was to leach the acid (tannic acid) out of the acorn powder. It causes a bitter taste and is poisonous. They would leach it by putting the powder in a water-tight basket (which is a basket that won't leak), and they would pour HOT water over it many times. They would taste it occasionally to make sure the acid was gone.