Locust and black walnut. Fresh cut black walnut will have a white sap ring that will turn dark brown as it ages. Black walnut will make a good firewwod right up until the very coldest of the winter. Used it for three years in a row. It burns hot enough but the heat demand in really cold weather causes more frequent trips to the wood pile. The best burn time I could get at -20 was 8 hours in my gasifier. Runs at about 20.2 million btu per full cord.