I don’t recall ever seeing anything about ground squirrels, but I do recall speculation about root intrusion beneath the slab from trees adjacent to the failure area. Those roots may have contributed to failure of the underslab drains and allowed that area beneath the slab to erode.
Remember the pics of the drains in the sidewall not jetting out water like they did in the rest of the spillway.
Yes I remember the sapling incursions but as the quote says the substrate condition and how the design and design administration failed to treat it was the main issue as I saw it.
The exchange about failure came after we were alluding to another issue entirely and that was the earthen dam itself, separate from the spillway. That dam was leaking and no one wanted to talk about it.