American prison is over that ravine (6)
I believe the answer is:
canyon
'ravine' is the definition.
(canyon is a kind of ravine)
'american prison is over that' is the wordplay.
'american prison' becomes 'can' (slang US term for prison).
'is over' says to put letters next to each other.
'that' becomes 'yon' (archaic term meaning 'that').
'can'+'yon'='CANYON'
(Other definitions for canyon that I've seen before include "Deep valley with steep, even Grand, slopes" , "gully" , "Defile" , "geographical feature" , "'Deep ravine, gorge (6)'" .)