Dear Bryan: As I said, they did use crude stone mortars and pestles. But to make ceramic cooking vessels, you have to know how to get the high temperatures to turn the clay into ceramic. I have seen a potter make very nice stuff in a large pit covered except for slanting channel so wood could be added until sufficient charcoal formed. Air could enter through wood channel, and a vertical flue in center to let smoke out with adequate draft.
I don't know how he judged when interior was hot enough, but then both wood entrance channel and flue were stopped up and left for a couple days. There was nothing he did that the Indians could not have done if they had known the procedure.