Do USAF fighter jets go supersonic over land?
Generally speaking, FAA does not allow supersonic flights over land except in special restricted military flight corridors. These are called High Altitude Supersonic Corridor (HASSC) in the US. For example, the one near Edwards AFB is:



NASA also mentioned about supersonic flights:


  The F-18s flew in Edwards' High Altitude Supersonic Corridor at 32,000
  to 40,000 feet for the supersonic runs.


However, I read that FAA's jurisdiction is only until 60,000 feet, hence above this altitude, there are no speed limits:


  According to the FAA regulations the controlled airspace extends up to
  60,000 feet. Anything flying above may fly at “unlimited speeds.”




During 9/11 attacks, US Air Force had its aircraft fly supersonically over mainland.