That's black hickory not black walnut. The nuts look similar when the husks are still on them, but if you look close the husk on a hickory nut peals off in 4 pcs like slices of an orange where as a walnut husk peals off in chunks like you're trying to peal or skin an orange. If you look in the yard you will probably old brown wedges of the hulls. That log is worth more as firewood than it ever would be for lumber. Black hickory burns pretty good, but you need to get it cut and split so it can start drying out. It likes to rot pretty quick, and the longer it takes to get it dry, the faster it will rot. If I cut one in the winter time (sap is in the roots, no the tree) and get it split in the spring, I can burn it the following winter. If it sits on the woodpile, by the end of its 2nd season its starting to rot and by the time the 3rd season arrives, its too far gone for me to bother messing with.