Mountains seen beyond delta in Highlands (6)
I believe the answer is:
sierra
This might be a double definition.
'mountains' is the first definition.
(I've seen this before)
'beyond delta in highlands' is the second definition.
I know that 'delta' relates to this answer.
'seen' is the link.
Can you help me to learn more?
(Other definitions for sierra that I've seen before include "Spanish word for a mountain" , "mountain area" , "Vehicle" , "International codeword" , "Spanish range of mountains" .)