To be correct, the jeep has 6k miles on it. I'm completely baffled as to what caused it to happen. Like WTF said, it hasn't been wheeled hard (Spring Creek, a few Moab trails, and this trip).
To walk you through it, we wheeled to the top of Twin Cones, no problems at all. On the way down, had it in 4low, 1st gear most of the way (Manual tranny, 4.88 gears). I was letting the engine do the holding back most of the way, assisting with brakes when there was a drop.
We we're at the last switchback to flat road when I dropped off probably a 8" tall rock coming around a corner. I had it turned close to all the way left to make the switchback. I heard a pop, and turned back to WTF to ask him if he heard anything, he said no, so I went about a foot forward. That was when it was clear that it was metal on metal, so I shut it down and found the carnage.
I'd like to figure out the true origins of what caused this, but can only speculate right now as to the cause. I'll go lay out the shaft and get some good pics and post them up. Maybe somebody can come up with a good guess.