It is propertied by some that there is a relationship between extra-terrestrials and covert elements of the U.S. military working side by side in these underground bases. After the threat of nuclear annihilation, many underground shelters were built for emergency purposes. Not only is being underground a protection, but can stifle the enemy in pinpointing your location. Underground bases have other practical uses such as waste and weapon storage, high-tech research, computer and command centers. The Federal Reserve and the Denver Federal Center are underground facilities.
Nuclear waste is store underground, such as the Yucca Mountain underground storage.
Many defense contractors have underground research facilities such as MacDonald Douglas and Northrop. There are many similar building facilities in remote areas all over the Southwest United States without any identifiable signs or markings indicating who owns or runs these facilities. Area 51 has been said to have major connecting underground facilities and has been said to go down many floors into subterranean levels. There is without a doubt many hidden underground bases within the United States and throughout the world. There are people who have developed these bases for the U.S. Government that have come forward to tell the public their stories as well as outside researchers who have dedicated time and published books on their discoveries of these hidden bases.