Thirty days before gold state's capital (6)
I believe the answer is:
juneau
'state's capital' is the definition.
(capital of Alaska)
'thirty days before gold' is the wordplay.
'thirty days' becomes 'june' (month with 30 days).
'before' means one lot of letters go next to another.
'gold' becomes 'au' (Au is the chemical symbol for gold).
'june'+'au'='JUNEAU'
(Other definitions for juneau that I've seen before include "Alaskan port" , "state capital" , "Capital of Alaska" .)