I believe this fungus is called a conk. It's actually the sign of ill health for a tree. I've known many artists that collect conks, dry them and then paint on them.
In the Rocky Mountains I have seen these conks get amazingly large.
Journey through 2009 with me! I belong to a group of beginning to advanced photographers and we started these blogs to share photos of our lives. Our professional photos are on our websites, our personal side is here!