Crucifix site 3: a WTFite

So, I’ve introduced you to the sediments at the Crucifix Site, and the faults which cut across those sediments.

Today, I would like to show you something else that I found there, and ask you to tell me just what the hell it is.

Here we go: an outcrop of the volcaniclastic sediments in this area (stratigraphically beneath the Bishop Tuff), where you can find orb-like hollow structures in the weakly lithified rock. Here’s a couple:

Zoomed-in a bit on the biggest one:

I excavated it from the surrounding volcaniclastic sediments, and popped it out:

Rotated slightly:

I have a guess what’s going on here, but I’m by no means certain. Any ideas from the peanut gallery about what this strange thing is?