Hastened, say, to return in Sierra? (5)
I believe the answer is:
range
'sierra?' is the definition.
(sierra is a kind of range)
'hastened say to return' is the wordplay.
'hastened' becomes 'ran' (I've seen this before).
'say' becomes 'eg'.
'to return' says the letters should be written backwards.
'eg' backwards is 'ge'.
'ran'+'ge'='RANGE'
'in' is the link.
(Other definitions for range that I've seen before include "Area for shooting practice" , "Scope; line of mountains" , "Compass, extent" , "Variation within limits" , "Area of variation" .)