I noticed several similar "spikes," just not as centrally located on the trail. I wonder if they are remnants of logging winches or other infrastructure that were cut off at ground level, then the ground sank around them. Does anyone care about this? There are many parts of the trail with exposed roots and rocks, where you know to be careful, but a nub of metal in a smooth area is a hazard in my opinion. You don't expect it to be there.