This is a gray tree trunk, did some hue adjustments, layered above, converted to B&W, and partially erased through. I have had a fascination with tree trunks since I was a teenager and saw a Disney program where several artists drew their versions of trunks. It was neat and inspiring.
I love them, too. There's just so much going on in the roots of old trees. I think this is a nice effect here because it really separates out the gray tones and makes it more three-dimensional. Good stuff!