Far side of oak tree backing border state (7)
I believe the answer is:
kashmir
'state' is the definition.
(I've seen this before)
'far side of oak tree backing border' is the wordplay.
'far side of' suggests the final letters.
'tree' becomes 'ash' (ash is a kind of tree).
'backing' says the letters should be written backwards.
'border' becomes 'rim' (I've seen this before**).
The final letter of 'oak' is 'k'.
'rim' in reverse letter order is 'mir'.
'k'+'ash'+'mir'='KASHMIR'
(Other definitions for kashmir that I've seen before include "Himalayan region" , "Territory disputed between India and Pakistan since 1947" , "disputed area" , "Himalayan territory" , "disputed Asian region" .)