In the NV dev diaries they said that Brotherhood wiped out the NCR's gold deposits, but they did not said which chapter. I assumed it was the lost hills chapter because the Mojave chapter does not mention it at all, but apparently the lost hills chapter does not exist:

From the wiki

"In contrast, the Brotherhood of Steel is a mysterious techno-religious organization, with roots in the US military. While few in number, they make up for this with their arsenal of pre- and post-War technology: They have laser weapons, Power Armor, surgical enhancements and combat implants. Unlike the NCR, the Brotherhood is not interested in conquest nor in saving humanity, but instead in maintaining their secrecy as well as preserving and developing technology. However, by the time of New Vegas, the only Brotherhood chapter on the West Coast exists in the Mojave Wasteland and not the Core Region."

What happened to that BoS chapter?

What's canon?

Obsidian likely didn't want to touch Fallout:Tactics because of it's contreversial canon status. with Bethesda explicitly stating 'The high level events of Tactics are canon'. But what explicitly is canon is anyones guess. Plus, I'm sure the Brotherhood members who went East to Chicago are now seen as dead or traitors, not unlike Lyons and his chapter.

Lost Hill does exist, it's just in a state of war with the NCR, Lost Hills Bunker is just outside Junktown, so they're likely in the fight of their lives trying to keep the NCR out.

Edit: Whoops I was thinking 'Core' is the center area of the US. My apologies.

Edit 2: I'm sure the Core chapter is largely gone if not already dead. Since the BoS are in a war with NCR in their own lands. They may be dead already.

Edit 3: Don't trust that image, that's a user made one. Fallout: New Vegas states the NCR is comprised of 5 states. So that map is wrong/out of date.

http://fallout.wikia.com/wiki/Core_Region

Bear in mind that the wiki can be edited by anyone, and does not claim a source for its claim that the WBOS is wiped out.

I'm not aware of such a source that makes that claim

I'm removing that part and putting it as a query on the discussion page.

It has to just be speculation.

Is the BoS still around in the Core Region?
We don't know.
Are they gone?
Likely.

That article needs a serious overhaul overall, it's a nice effort and props to whoever put it up but it needs some serious refinement.
It's highly unlikely that the West Coast Brotherhood of Steel has been wiped out, or somebody in the Mojave chapter actually would have commented on it.

They arn't wiped out. If you can find that quote word for word in an article written by the devs or video that has them talking about it then wiki is bullcrap. I doubt Obsidian or Bethesda will kill off the BoS back west without a single mention of it in New Vegas. I just don't see it happening.

I've tried to clean up the history bit, but I'm too tired to do more.

Nice job, as far as I know everything under history is absolutely true.

What I'm more confused about is, if the the Core Region BoS are no longer active or are currently at war with the NCR, then who is making Gauss Rifles, Super Sledges, and other high tech weapons? That was how they survived in Fallout 1, trading weapons nobody else could make but them, for food and other materiel they need.

I'll take a look at the article in a bit, see if I can't tighten up the writing and fix parts that are obviously incorrect.

I don't see how the original chapter would be completely wiped out maybe beaten back but not wiped out.

Alright, I overhauled everything relating to the Brotherhood, gave the Factions section a facelift (and added Enclave). Let me know if I got any BoS facts wrong, and I'll fix them.
Gonna add the Master to Core Region Factions as well, I think.