Bonneville Salt Flats state (4)
I believe the answer is:
utah
'bonneville salt flats state' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for utah that I've seen before include "A hut marks the State" , "State, Mormon settlement" , "Bryce Canyon US state" , "State of Western USA" , "US state, capital Salt Lake City" .)