Hard to say. The Ceporah Tower is older even than the High Elves' arrival on Summerset from Aldmeris. Its interior reminds me of a big snail or clam shell, and water and fossils also seem to be strongly associated with it, too.

I'd venture a guess and say either it's an Ehlnofey (Earth Bone) body or an old Sload structure of some kind.

of Coral perhaps?