Great plains of Argentina (6)
I believe the answer is:
pampas
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">great plains of argentina</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for pampas that I've seen before include "Vast plains of South America" , "Great plains of S America (6)" , "Argentinian plains" , "South American grassland" , "Great plains of Argentina" .)