I think it might have changed from edition to edition. Last I checked the Happy Hunting Grounds had been changed to the Beastlands, which is (as El Gallo said) in between the Neutral Good plane of Elysium and the Chaotic Good plane of Arborea. The key feature of the Beastlands is that all the petitioners take the form of intelligent animals; not sure if that's how the Happy Hunting Grounds worked.