It doesn,t look like the tree had time to grow around it. No one has yet wondered if a round was chambered.
I think that’s it - that tree doesn’t look 100 years old, and would have grown around the gun.
I'm just saying that rifle would look just as weatherbeaten in less than 40 years as it does now, judging by the furniture. I've seen dilapidated fences all over my local part of Nevada in that shape that I know aren't more than 20 years old. Winter snow and searing Summer heat thrashes exposed woodcut like you can surely appreciate.
... Come to think of it, I have a wood plank fence on my property that's only 8 years old that would look just like that rifle stock in a few more years if I hadn't have sprayed it down good with boiled Linseed oil. I've had to repair that fence three times already. Nails are blackened and loose everywhere down the fence line.
I would like to point out that rifle could easily have never left that spot -- standing or not -- in over 100 years despite whether it's true or not that it had actually been there that long: I'm absolutely certain there's parts of my state that hasn't had a human footstep nearby since the last Pleistocene giant armadillo hunters moved through there 145,000 or more years ago during the last Ice Age.
(On that note, I met a fellow Nevadan at a Safari Club meet in Reno who found a big flint spearhead out in the local desert, ultimately thinking it was from one of the local Indian tribes. A paleontologist at UNR took one look at it and said it's easily 100,000+ years old.)
That area where the rifle was found is actually one of the prime Elk hunting zones that big game hunters pray to get assigned a permit tag for in the yearly NDOW lottery. I'm betting that's lots more like what the story is behind that rifle being left there, rather than the notion it was forgotten there over 100 years ago by a prospector: You drive off leaving gear behind and once you get a half mile away from where you were you'll never find your way back to the spot you were in. At least in the days before GPS that is.