In the grey light of the Nevada dawn, in a parking lot in front of the courthouse, a small group of people board a white bus with tinted windows. At around ten minutes to seven, just as it does every weekday morning, the bus pulls out of the lot, noses through the little town of Alamo and turns out onto the highway.

The white bus speeds past the sticker-encrusted green metal sign that reads "Extraterrestrial Highway"; past the "Alien Research Centre" with its giant metal alien statue, past the graffiti of bug-eyed space invaders and onto an unmarked dirt track where it kicks up a cloud of dust visible for miles around. Finally, it slips in among the hills and passes through a hidden security checkpoint, delivering its passengers to another day's work at Area 51.

For all its near-mythical status among UFO obsessives and conspiracy theorists, Area 51 – properly known as Groom Lake or Homey Airport – is a real place. To the people living in the small towns and farming valleys nearby, its brooding presence is a normal part of life, something accepted if not always eagerly discussed.

Now, though, those people are frantically preparing for thousands of outsiders to descend on the area, after some 1.9m people said "yes" to a viral Facebook event calling on attendees to storm the base on Friday and "see them aliens".