I am a California enrolled agent experienced in preparing returns for Same-Sex couples.
The authority for the recognition of these marriages are based within case law.
Source: Hollingsworth v. Perry
See specifically page 16
See specifically sections b and c
Since the 2008 taxable year same-sex married couples had to file their California tax return either as married filing jointly or married filing separately in contrast to federal filing requirements.
As of 2013 no difference exists between California and federal.