This part of the range is huge, they say (6)
I believe the answer is:
massif
'this part of the range' is the definition.
('massif' is part of 'range')
'huge they say' is the wordplay.
I cannot really see how this works, but
'say' could be 'as' (I've seen this in other clues) and 'as' is located in the answer.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for massif that I've seen before include "Geographical formation" , "highlands" , "Compact group of mountains" , "Compact mountainous area" , "Geological mountain formation" .)