After listening to many Project Camelot interviews, and all this talk of massive super deep underground military bases, underground reptilian bases I begin to question the validity of such claims. (Bill Deagle, Pete Peterson, etc.)
Especially the claims of bases 4 miles deep and deeper.
Your typical oil driller knows, that on average every 1 mile you drill down into the earth the temperature in the earth rises 25 degrees centigrade. At 2 miles deep its 50degrees, 3miles 75degrees, and 4 miles 100 degrees!!! At 4 miles an underground base would be uninhabitable being the temperature of a boiling cooking pot!
Now obviously geography plays a role as well, but consider the temperatures across the US at a depth of 6km (3.72 miles).
Notice how most of the continental US at a depth of 3.72miles sits between 100-200 degrees centigrade.
A base 1 mile underground at an average temperature of 25 degrees is conceivable...anything below that I highly doubt is possible, unless you have multiple power plants providing an insane amount of cooling. Or your in one of those few isolated spots where it actually happens to be cool. See green spots on map above.