Nevada Test and Training Range, Lincoln county, NV
Conspiracy: There's a stockpile of aliens somewhere in Nevada
And no, we don't mean people at the $5 blackjack table at 7am. Those are lowlifes and deadbeats, not extraterrestrials. Although they are often not human-looking. Allegedly, all those UFOs and aliens spotted over the years are being hoarded at Area 51, a top-secret Air Force base 85mi from Vegas.
Scientists are said to use the remains of crashed UFOs to reverse-engineer their futuristic technology... or the "true story," if you think Men in Black is based on a true story. Other theories speculate about lab tests on aliens, both alive and dead, or even working with aliens to create new technology. If you can't beat 'em, keep their corpses in a secret military base and reverse-engineer their technology. That's what we say.
It also doesn't hurt conspiracy theories that airspace restrictions prevent even Air Force pilots from flying overhead, and that the CIA didn't publicly acknowledge the base’s existence until July 2013. So there's that.