An account in Clearwater County, Idaho

I was archery hunting in Idaho not far from Headquarters Idaho, actually between Township Saddle and Township butte, when I encountered something that I have never experienced before in the mountains. I heard something heavy running ahead of me to my left as I was walking up on old railroad grade that has been used by 4-wheelers. My first impression was it may have been an elk, but I didn't see what was making the sound. I had walked about 1/4 mile from my partner and was closing in on an area where we had seen elk earlier in the week and thought I would try to push ahead to get into the area I had seen the elk. I was walking very quietly when I heard a sound that I thought was a bird flying overhead. I looked up since the sound came from in front of me, when I heard something hit a tree and then the ground behind me. As I turned around, I noticed a branch on a small tree behind me that was moving as if something had hit it. Before I could walk back to the tree which was only about 15 feet behind me, the branch had stopped moving. There was no wind and it was very calm, and very silent. When I got to the tree, the only think that I found was a large chunk of bark that was laying on the ground. I found this to be unusual since it came off a large tree such as a ponderosa pine as the bark was about 14 inches long, about 6 inches across and about 2 1/2 inches thick. This area has been logged in the last 40 years and there were no trees in the area with a girth which would have produced bark of this size. At this point, it was getting late in the evening so I decided to head back to the 4-wheeler and my hunting partner. I called him on the radio to see where he was. He said he was waiting for me at the 4-wheeler, still about a 1/4 mile away from me. I found nothing else on the trail which would have produced this sound and was wondering if this could fall into the phenomena of others who have experienced similar situations. I was a bit cautious as I walked back down the trail but heard or seen no other anomalies.