Sounds like it could have been or be a sea turtle nest. (Sometimes they have to be relocated depend on where the turtle lays the nest) That is typically how we mark them off! Though I volunteer for NEST and go no alert today!
Yea the 3 feet deep thing throws it off! The four stakes and police tape are exactly how we mark the nest. And if it was a leatherback turtle nest those are very huge and would be about 7 feet across because the measurement we go by is if you can “fit in the pit” it’s so big it’s a leatherback turtle! But 3 feet deep is weird. Fill in the hole!!!! It will mess up a real turtle if it comes!(Sorry had to edit. Got my turtles mixed up!!)