Mountainside stones (5)
I believe the answer is:
scree
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mountainside stones</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 scree that I've seen before include "Loose debris on a mountain slope" , "Small loose stones on a mountainside" , "bits of rock" , "Rock fragments at cliff foot" , "Safeguard" .)