US grassland (7)
I believe the answer is:
prairie
'us grassland' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for prairie that I've seen before include "Treeless grassy plain, in the old West perhaps" , "-- Dog; -- oyster" , "this oyster produces an egg" , "Wide grassy plain" , "Continental grassland of N America" .)