Detritus on the side of a mountain (5)
I believe the answer is:
scree
'detritus on the side of a mountain' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for scree that I've seen before include "Stony hillside" , "Mass of loose rocks at the base of a cliff" , "Rock debris at the base of a cliff" , "bits of rock" , "Loose debris on a mountain slope" .)