Out of curiosity I just took out the current Las Vegas sectional.
Where you describe the "airbase, not shown on any map", it shows a "Private" and "Unverified" Airport, and "towers". There's also a small note saying "Prior approval required from Dept. of Energy" but no contact number or frequency.
Which basically means that there's a government airfield there which doesn't want uninvited guests - but we probably knew that
Every government has places like this, but that doesn't make them any less fascinating to the nosey observer.
G