Ridges of sand (5)
I believe the answer is:
dunes
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ridges of sand</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 dunes that I've seen before include "Hills of windblown sand" , "Sand hills by the sea" , "Nudes behind sand-hills" , "Ridges of sand" , "beach" .)