A Pile of Sawdust

Fresh sawdust chips on a trunk.

I noticed piles of fresh sawdust beneath a dying canyon live oak when I was chasing some cows out of The Pasture of Death last week. After unchaining the gate and opening it wide, I snuck through the forest to get behind the cattle and did a chicken dance to get those bossies moving into the proper pasture.  While waiting for the cattle to walk through the gate, I went back to look at the mysterious sign.

Exposed hole after  I pulled out most of the loose sawdust.

The chips of light brown wood were shredded into pieces one to two inches long and about 1/8" wide and formed an elongated pile on the ground about 2 feet in the downhill direction, 6 inches wide and an inch deep. There was another pile on another side of the tree.  On the mossy trunk about 2 feet above the ground piles were two round circles out of which were hanging similar sawdust pieces.

My fingers showing the depth and general size of the hole. I've got small paws.

I poked my fingers at the loose sawdust and started pulling it out of the holes in the trunk.  The holes were about 3" in diameter and two inches deep.  I did not completely excavate the holes because I needed to run back and close the gate before the rest of the herd decided to check out the other side of the fence. But my prodding indicated that the holes extended another inch or so downward beneath the bark.

Second hole on same tree after I pulled out some of the sawdust.

I have some idea of what may have made these holes, but I thought I would give you a chance to guess. So, what do you think made these holes?  Ask me any questions you want.