Los

Los is what remains of Los Angeles after the Great War, in place of the bustling metropolis it once was, the city has been reudced to a ghoul refuge, inhabited by ghoul fanatics who kill all humans who wander into the city limits..., you can find Harold here but all he does is send you on a quest to find his missing body parts. The Secret Vault built by Vault-Tec for top secret Forced Evolutionary Virus research can be found under Los.

Inconsistency
This is of course totally inconsistant with Fallout and Fallout 2, since Los Angeles appeared as Boneyard in FO1 and was mentioned as one of the states of the New California Republic in Fallout 2. Moreover, the Los Angeles Vault was not some FEV research Vault kept secret by Vault-Tec, but a demonstration Vault.