Wiktionary
lower 48
n. (context US geography English) the contiguous continental states area of the United States of America, comprising 48 states in number, and the District of Columbia, excluding Alaska and Hawaii.
Usage examples of "lower 48".
So it's not an automated, unmanned franchulate like you normally see in the Lower 48.
I believe the reason nobody has ever found this city is because it is hidden in the most remote section of the lower 48.