Range sent back, somewhat bizarre I see (6)
I believe the answer is:
sierra
'range' is the definition.
(sierra is a kind of range)
'sent back somewhat bizarre i see' is the wordplay.
'sent back' is a reversal indicator.
'somewhat' indicates a hidden word.
'arreis' is hidden within 'bizarre i see'.
'arreis' written backwards gives 'SIERRA'.
(Other definitions for sierra that I've seen before include "Spanish word for a mountain" , "Comms code S" , "Nato alphabet 'S'" , "A Spanish mountain chain (6)" , "Range of mountains with jagged peaks" .)