That all assumes the deity was ever a creature instead of just pure myth. If it was a creature at one point, it would be a very stone, earthen focused one that has ties to olden Earth Elementalkind for it to have gotten its status.
I'm kind of leery of the "farce from a deity" because then it could possibly be demonstrable, where the main idea is a belief in something not-proven in face of proof of other things. Basically isn't what I'm looking for/wanting to get outta this in terms of story, in short.
Now maybe if it was a farce long ago that grew out of control, then died off and was pretended to have never happened by said deity that tried to pull it off, maybe, but still brings it back to "still possibly demonstrable if deity feels like it," and none of them have the domains I'm looking for in mind. Well, not all of them at least, some do have one or another, but really never grouped beyond a stray one. Thinking on it, I'm liking the idea of leaving it all very vague.
Idea in my head was that the "deity" is claimed to have spawned Earthen Elementalkind. The idea died down over generations though, it being a rather old idea, due to never being demonstrable but some still hold the belief. Probably shown as a goddess because "Stone Singer/Sister," "Mountain Mother," or "Rock's Rookery." 'Dem alliterations. And most creation stories relating to deities tend to deal with goddesses, if I recall.
I actually have most of the idea bolted down in my head already, and a buncha fun cultural points about it thought out, but I don't want to spoil it until the game.
Its not really meant to be a focal point of the character though, just a thing he does which affects other things he does, but by no means a defining trait. Unless you consider it I suppose, I just figure it a minor write off on a cultural note, something that gets brought up once or twice, or maybe shown in the light at a time or another, but nothing really brought about of it.
EDIT: Holy crap I wrote a lot more than I thought. Sorry 'bout that.