It’s a classified military installation. Those that know for sure don’t talk and those that are talking are probably talking out their ass.

It is known that it has historically been used as a test and research location for highly experimental stealth aircraft. They probably do EM sensitive research and testing there now, but I suspect that the really interesting stuff is happening elsewhere due to how well known and watched it has become. It’s probably more of a decoy than anything else at this point.

Long ago, I remember hearing rumors about a more secretive base a bit west of Groom Lake and south of the Cheyenne Mountain complex. If true, that’s probably where the really secret stuff is happening now. No clue what happens there.