The way that Tethys and Nubium craft planets is 100% by natural means, just with their time transcending abilities they are able to steer things in various directions with minor tweaks here and there, giving the illusion of them having no input at all. It gives them somewhere rather lovely to hang out and blend with the natural beauty of the planets they create as they go though.

But here we have Tethys hanging out on a mesa. Something that she or Nubium will have put together a few billion years prior to this picture!