The job is done!
As it turns out, I did NOT have any concrete mix on-hand after all. So, we went to the farm store and bought sand. Those holes were DEEP. We filled with sand, topped with some dirt we found “around” and then I leveled and tamped it all with the tractor bucket. Will keep an eye on them for settling.
I am fairly certain we got them all, I’ve been over the place pretty thoroughly.
So glad I found them before somebody got killed!!!