These mountains tending to shake? (5)
I believe the answer is:
rocky
This clue is a double definition.
'these mountains' is the first definition.
(Rocky Mountains, North American mountain range)
'tending to shake?' is the second definition.
(Other definitions for rocky that I've seen before include "lacking 15d [STABILITY]" , "Unstable (like North American mountains?)" , "likely to collapse" , "Unsteady, unstable" , "Film" .)