So, I think Uranus is a Gravity Control device that creates artificial Gravity Fields via Electromagnetic manipulation.
If we look at Lulusia, everything is being forced straight down, even the sea itself: I believe the same happened to God Valley, as well as Davy Jones.
Cursed by the Devil = Uranus knocked Davy Jones into a high-gravity area he can't escape. The treasure "sinks" there because it's effectively a Gravity Well: Davy Jones literally can't escape. In this scenario, Davy Jones would have received the Eternal Youth Surgery, from Law's Fruit, and is effectively immortal in terms of aging, but can die, like the Gorosei.
Rocks seeking out Uranus on God Valley makes a lot of sense, since he's announced himself as a disciple of Davy Jones. If Uranus is what took out Jones, it makes sense Rocks would want it, especially if he knows Jones is still alive.
God Valley fits as a name, too: Uranus is the God of the Sky, so it's an ironic name, if Uranus knocks Islands down to the Sea Floor using Gravity Wells/Fields. God "Valley" as in Uranus knocks everything down to the "valley" of the Ocean Floor.
@Paperchampion23 Your Uranus theory is looking really solid, IMO. Garling talking to the Gorosei reminds me of York talking to them about the Mother Flame.
I think Luffy's going to straight up go to Davy Jones' Locker.