Another piece of the puzzle:
Yesterday evening, we had a strong storm pass through, lots of rain...we needed it, drought-like conditions here for quite a while
The dirt patch in my yard where dozens of the holes are were submerged after the storm...and the holes are still there...MUCH less amount of holes than yesterday, but there, and "open for business"...several of them
So...what did they do, and how did they survive, while their burrows were submerged, for several hours (?)
Do they have gills? Did they drown? Do they flee the burrows, and head to the grass, until the waters recede?
BTW, these holes are all throughout the grass lawn, as well, just harder to spot.