Mountain range spread endlessly upwards (4)
I believe the answer is:
alps
'mountain range' is the definition.
(Alps is an example)
'spread endlessly upwards' is the wordplay.
'spread' becomes 'gap' ('gap' can be a synonym of 'spread').
'endlessly' indicates the central letters (the ends of the words are removed).
'upwards' becomes 'lps' (I can't explain this - if you can you should give a lot more credence to this answer).
The middle of 'gap' is 'a'.
'a'+'lps'='ALPS'
Can you help me to learn more?
(Other definitions for alps that I've seen before include "& 11 their highest peak" , "With pals in great mountains" , "Mountains in Central Europe" , "High mountains" , "European mountain chain" .)