Tonight while riding said trail, at the base of a committed rock roll, was placed in the track, a large broken off base of a jar.
Luckily, our lights picked up the distinctive blue glass, which looked like tinfoil from the top of the roll.
I climbed down and realized it was glass the heavy weight kind you would get from a big ass jar of pickles, or something like that. It was just the base.
There were no other parts of the jar around, as I did a quick scan.
Be aware. It was very strange. So out of place.