Los Angeles vault

Los Angeles was the site Vault-Tec chose to build their demonstration Vault. Located in the southern district of the City of Angels, it was a fully functional shelter, though it's design varied from the one used later for West Coast vaults (and the ones on the East Coast for that matter). As a demonstration, it was extremely succesful and jumpstarted Vault-Tec into Project Safehouse.

During the Great War, people hid in the Vault, which functioned as intended - it protected them from the hazards of the nuclear holocaust. Years later, it opened, and the inhabitants that emerged into the Angels Boneyard eventually split. Some formed the Adytum, others the Regulators, while others chose to explore the wastes.

It was the latter group that was found by the Master's scouts, thus giving him the location of the Vault. Relocating there, Richard Grey permanently integrated himself into the Vault, slowly growing into it, neurolinked to the central computer.

Entrance
The entrance to the shelter went through a small cave, linked to the Cathedral's basement. Upon entering, the differences in layout were evident - the airlock was much smaller, the EML-2 room was designed with additional windows and the main hall was one large chamber.

During the Master's reign, two Nightkin stood guard at the entrance at all times.

Level 2
The second level also differed in layout, with the elevator located to the side, not in the center. It is possible the supermutants made alterations to the original design. In 2161, the second level housed a chapel, barracks for Supermutant guards, a large experimentation lab, where mad scientists worked on awakening the psionic potential in humans, the aforementioned psyker holding cell and test subject cells.

Command Center
The third level housed the heart of the Unity. Here, apart from the most elite Nightkin detachment and their leader, Vicious, the Master resided, united with the Overseer's command chair. It is here, where the elevator to secure storage was located.

Nuclear Warhead Storage
The deepest level of the demonstration Vault was where the Master kept his ace-in-the-hole weapon. Should the Unity face an enemy it would not be able to defeat, the supermutants would deploy one of the last few remaining nuclear warheads against them. For security reasons, the key to the console was kept in the possession of the supermutant Lieutenant.