Atomic Postman
Vault Archives Overseer
Hmm. There's the Bethesda route to give them something Arthurian. With that in mind I guess Avalon would work best, a distant and fabled place far from home, and the Brotherhood has effectively gone there to die since (not counting Midwestern or DC BoS) this is their furthest extent prior to the NCR-Brotherhood War. And it seems like you're going for something similar to that since you implied that this bunker would be the source of the Colorado BoS that has forgotten Maxson's name, presumably after they conquer Boulder and assimilate tribals. But Avalon may be too on the nose.
Alternatively you could go for something Biblical. Gives it a fantasy feel, and also a literal 'knights on crusade' vibe. Gilead maybe, since that was the portion of Israel not technically a part of Israel - distant, across the Jordan, with the understanding at the time of conquest that the Gileadites would have to leave this land to help the main body of the Israelites. I could suggest other potential Biblical names if you're interested, though that doesn't really seem to be the Brotherhood's bag so it would be a bit odd.
You could cheat and have their be some Poseidon thing at the array so they name it after a Greek god.
In terms of English type names which I think is more what you're getting at...
Citadel is right out of course, but you could name it any number of synonymous things that imply their isolation and this as a forward operating base. Star Fort would gel with the Nexus, but the name sounds a bit lame. Redoubt doesn't sound great. Castle Rock sounds kind of cool, but of course is already a place in Colorado so it might by a bit odd.
You could go the same route as Lost Hills or Hidden Valley by naming it after actual local features. Looking around the actual VLA location... Lone Mountain, Lion Mountain, Blue Mesa, Enchanted Tower, Bear Mountain, Red Rock, Horse Peak. Lone Mountain and Blue Mesa are probably my faves. Though this also assumes that the Nexus is at the same place as the VLA.
Lone Mountain too close to Big Mountain and Blue Mesa too close to Black Mesa
How about Lone Mesa?