M Cave and the Unexplained Disappearance of Kenny Veach (2019)
nevadamagazine.com
nevadamagazine.com
As far as the M Cave weirdness - people say all sorts of stuff on social media for attention. As they say, "Pics, or it didn't happen".
And actually - it has 2 "M Cave" candidates which people have visited since. One - probably the wrong cave (high up, when M Cave was ground level). The other one, I feel it's a tall order that it's been "filled in". While strange, the M-Shaped cave found mostly filled with different colored sedimentary rock, it doesn't resemble any kind of man-made mortar/concrete/etc.
The military's style is to just pour high PSI concrete into a mold and call it a day, not to try to emulate natural sedimentary rock and half-ass block a cave in a way that a prybar can get past.
All in all - the real M Cave (if indeed there was one to begin with), it's appearance and approximate location is only known to someone who is not likely to ever be seen again.
Sorry for the aside. Hope it's relatable.
I also think it's most likely that the man didn't want to be found, sadly. He wouldn't be the first.