Organise a run over some mountains (7)
I believe the answer is:
arrange
'organise' is the definition.
(arranging is a kind of organizing)
'a run over some mountains' is the wordplay.
'a run' becomes 'ar' (I've seen this in other clues).
'over' means one lot of letters go next to another.
'some mountains' becomes 'range' (I've seen this before).
'ar'+'range'='ARRANGE'
(Other definitions for arrange that I've seen before include "position" , "Order, plan or design" , "Dispose" , "Set in place" , "Put in neat order" .)