Just another point to add to the discussion:  the archeological record of the Pacific Northwest peoples, which goes back more than 10,000 years, does not include any ceramics, even though local clays are abundant and accessible.  Assuming that these folks migrated from Asia (the traditional interpretation), it appears to me unlikely that such an important technology would have been lost if already practiced.  All the usual uses of clay were fulfilled thru crafting other materials e.g.,  bark, reeds, tanned hides, stone/bone carving.

Eric Newman