I’d guess: domestic terrorism.
These types of facilities have been targeted before. The Stewart Mirror Lab at the UofA stopped doing tours for several years after being the target of a “terrorist” plot. There are quite a few folks who don’t like people building structures on the tops of mountains…
Any sort of “usual” terrorism doesn’t make sense. They have shut out the local LE completely. You do not do that if you are going after terrorists at a site.
And if someone planted a bomb there why not just say so? The person who planted the bomb knows the jig is up what with the helicopter and the FBI. Who are you keeping this a secret from? Plus, you want to talk to the staff there. Did they see anybody do anything off? Maybe package that wasn’t there before? And on and on.
What if someone dumped some anthrax near the entrance or something. Um, don’t you want to warn people who may have been exposed to see a doctor, take some precautionary drugs, etc.? Certainly don’t want them flying back home while their facility is shut down.
It is very, very hard to come up with any plausible explanation that doesn’t get into woo territory.
Woo #1. The US military had a “oopsie” near the site. E.g., a nuke fell out of a USAF plane or some such. They are in full CYA mode and don’t want anyone to know while they clean things up.
Woo #2. Being a solar observatory, they are experts on solar cycles which have been used to discount the stupid “the recent warming trend is just part of the normal solar cycle” nonsense. Trump sent in the FBI to shut down the place and destroy records. (This is more like Woo^Woo.)
The Sherrif referenced a bunch of people around antenna and work crews on towers that weren’t explained to him. The article considers the option of using that nice line of sight and the antenna farm to set up electronic monitoring.
It’s a simple, if relatively mundane, explanation for the limited facts available.
The idea about a surveillance device seems intriguing but there’s still oddities.
One of the linked articles says "With the capabilities of modern electronics and batteries, it’s possible that such a system wouldn’t even need to be hard wired. "
If you don’t need wires why risk putting it on such a site? There’s a lot of similar mountains around. Put it in a tree on one of those. Less likely to be noticed, etc.
I think that being wired is important.
The FBI has to be asking employees about what they might have seen, etc. So a lot of employees have an idea about what is going on. One of those, despite warnings, has to have blabbed to a spouse/friend/whatever and then the secret would be sort of out by now. Shoot you could post something anonymously on the Internet via the Tor browser.
Unless they are not asking employees, which would be very odd.
Even then why leave local LE out of the loop? Why keep the site shut down but with no security detail for at least a couple days? Etc.
If the concern is a possible intelligence device attached to one of the antennas, what possible reason would there be to evacuate the facility?
It’s also possible that they are just planning some secret test or exercise which would be visible from there, and so needed the area cleared. But then why did it take so long to get proper security set up?
This was my first guess, too.
They plan to roll out some new secret device,and don’t want it probed by high-tech equipment. That’s a simple, clean explanation. (But not as much fun as aliens).
As for the sudden rush and evacuation at the last minute…that’s explainable by standard human stupidity.
Somebody simply forgot to notice the observatory contains,say, electronic equipment which uses the same wavelength (or whatever) as the new secret device.
Wait, if the government is installing a secret monitoring device how come they are not using the same crew that wired the WTC for demolition? They managed to move tons of explosives, wire and whatnot into a building occupied by several thousand people with no one noticing. Seems to me that one little bitty sensor should be easy.