Again atop rocks in part of South America (9)
I believe the answer is:
patagonia
'part of south america' is the definition.
('Patagonia' is part of 'south america')
'again atop rocks' is the wordplay.
'rocks' indicates anagramming the letters.
'again'+'atop'='againatop'
'againatop' is an anagram of 'PATAGONIA'.
'in' acts as a link.
(Other definitions for patagonia that I've seen before include "Southernmost region of S America" , "Region of South America" , "far-off land" , "South American region" , "Craggy region" .)