arl, I'm not exactly sure what kind of wood it is, my dad built a retaining wall with it before I was born (so at least 22 years ago), and in the past few years it's use has not really needed and the area became overgrown. It's had plenty of time outside thought
and absorbs water really well, also it is not that dense, but that could just be from age. He say's he thinks it's either oak or pine, but could be just about anything.