Bunker area 25 km from the city (Manhattan area two), powerful - very powerful - underground construction under the guise of reconstruction of the airport. In terms of dredged material - a complex of several hundred thousand people, plus some kind of military infrastructure.
No official explanation: No (funny version that all airport requirements, with the exception). Unofficial version - rolls in conspiracy theories. Here and Masons, and a world government, and Satanists, as well as analysis of the frescoes and sculptures (really creepy and weird)
This underground city for the part of the elite, who would dare to stay on the continent after the explosion of the volcano. The location is perfect. Over the Rocky Mountains from Long Valley, on a plateau, in the heart of the country, the most protected from the tsunami. Surprisingly close to Yellowstone (you can omit further south, in some Albuquerque), but - for the spine, and if we impose on the map map of Latin American states, then everything will fall into place. Deleting the maximum under the "white man's zone". This is the person to whom it generally makes sense to fight for the continent. Airport leaves the possibility of a large-scale evacuation.