Campers must move - tent's beginning to fall off a cliff (10)
I believe the answer is:
escarpment
'a cliff' is the definition.
(thesaurus)
'campers must move tent's beginning to fall off' is the wordplay.
'must move' indicates an anagram.
'beginning to fall off' means to remove the first letter.
'tent' with its first letter removed is 'ent'.
'campers' anagrammed gives 'escarpm'.
'escarpm'+'ent'='ESCARPMENT'
(Other definitions for escarpment that I've seen before include "Precipitous side of hill" , "Face" , "Bluff" , "Long edge of plateau" , "Steep slope at edge of plateau" .)