for my $city ( keys %$location_hash ) {
   .
   .
   .

   printf "Before deleting: state=%s zip= %s\n",
      $location_hash->{ $city }->{ 'ST' },
      $location_hash->{ $city }->{ 'ZIP' };

   delete ($location_hash->{ $city });
   ### delete ($location_hash->{ $city }->{ 'ST' }) ;
   ### delete ($location_hash->{ $city }->{ 'ZIP' }) ;

   printf "After deleting: state=%s zip= %s\n",
      $location_hash->{ $city }->{ 'ST' },
      $location_hash->{ $city }->{ 'ZIP' };

} end for loop