I've just moved this post up to the top of the list because I added the long-anticipated pictures of Oak Leak Moth poop.
One of the hazards that California Coast Live Oak (Quercus agrifolia) trees face is infestation by oak leaf moths. My father educated me about this around the end of September with the main example being some trees on my parent's property: An older tree seems to have come through with a greater fraction of leaves intact but some smaller trees have been almost completely denuded.
Below are pictures of moth larval poop and an eaten leaf. The poop was caught up on a spider web, which is why it clumped together.