Obscure, formerly, in California (7)
I believe the answer is:
conceal
'obscure' is the definition.
(thesaurus)
'formerly in california' is the wordplay.
'formerly' becomes 'once' (synonyms).
'in' indicates putting letters inside.
'california' becomes 'cal' (short for California).
'once' put within 'cal' is 'CONCEAL'.
(Other definitions for conceal that I've seen before include "'Hide, keep secret (7)'" , "Place out of sight" , "hush up!" , "Keep out of sight" , "Screen" .)