Mystery object from the forest floor

A friend and I spent this afternoon exploring the west end of Griffith Woods. He noticed this very strange object lying on the forest floor, and he feels pretty sure that it is natural. Length is very approximately 5". The left-hand end (in my photo) had formed a hollow, conical shape, while the rest was covered in nobbly lumps. Does anyone "out there" know what this may have been caused by - perhaps by insects? Any suggestions?