Twin Mothers

Twin Mothers is a small tribal village in the American southwest. As tribal as tribals get, that's these guys. They do well for themselves, having skill in agriculture. They're the descendants of Vault 31, and their village is built on top of the Vault. The Vault itself has ceased working long ago, but it's still a holy place to the Twin Mothers. Hecate has a powerful influence here, but the tribe hasn't completely fallen under her sway.

Appearances in games
The Grand Canyon did not appear nor was mentioned in any of the published games, but was to appear in the cancelled Fallout 3 project by Black Isle codenamed Van Buren. It is not certain if it will appear in any future Fallout game, but it is known that Bethesda received all Van Buren design documents from Interplay and might re-use some of the background from them.