I have actually been thinking of where the Vault would be. I'm gonna go on the vault wiki and find a list, then we'll all decide on 3 of the best choices that Yttrium and Silly Cat, and me, choose from via PM.
Screw it! Lets just make a Vault up! The ones I looked at on the Vault Wiki wouldn't fit in the RP all to well. Unless Yttrium or Silly can find a suitable one.
Well you don't necessarily have to come from a Vault. You could be survivalists, or the descendants of people who were in a Non-Vault underground facilitiy when the bombs hit.
You could even just be people who lived in a small town that didn't get annhiliated by the bombs and wherein there was minimal post-Apoc Chaos. Hell we could do Alaska if that tickles anyones fancy and just say we're a group of people who were raised in a Weather Observatory in the middle of nowhere.
I think it would be a breath of fresh air to not be Vault Dwellers personally.
Since it's BEFORE Fallout 1/2/Tactics/3 we might even come out of a Vault already used anyway, if set in California that is.
Vault 6 has no known purpose and is set up in Washington State (Mt. Saint Helens)
Vault 8 opened just 10 years after the bombing, it had a GECK but we could have left immediately due to some political unpleasantries or something
21 is in the Mojave Desert and it's purpose is not yet known (Wont be known until NV comes out i assume)
Vault 34 The armory was overstocked with weapons and ammo and not provided with a lock. -Location Unknown
Vault 36 The food extruders were designed to produce only a thin, watery gruel. Location - Unknown
Vault 39 Original purpose unknown. Abilene, Texas
Vault 53 Most of the equipment was designed to break down every few months. While repairable, the breakdowns were intended to stress the inhabitants unduly. - Location Unknown
Vault 76 This Vault was designed as a control group for the vault experiment like Vault 8, intended to open and re-colonize the surface after 20 years - Location Unknown
Could even be Vault 13 cast outs, not like the Overseer wouldn't lie and just send some troublesome people away.
Those would probably stretch from the West Coast to just East of the Center of America i think.