Diane's arranged to leave US city (3,5)
I believe the answer is:
san diego
'us city' is the definition.
(I've seen this before)
'diane's arranged to leave' is the wordplay.
'arranged' indicates an anagram.
'to' is a charade indicator (letters next to each other).
'leave' becomes 'go'.
'dianes' is an anagram of 'sandie'.
'sandie'+'go'='SAN DIEGO'
(Other definitions for san diego that I've seen before include "Southern California naval base" , "Calif. naval base" , "Pacific port" , "Californian port" , "City of S. California" .)