Eugene Volokh looks at the California opinion:
The opinion is entirely based on claims under the California Constitution, and does not rely on federal constitutional claims. This means that the U.S. Supreme Court cannot review this; and it also means that a state constitutional amendment — which seems likely to be on the ballot this November — could overturn the decision.
Here’s the court’s reasoning, in a nutshell:
1. The California Constitution’s Due Process Clause and Privacy Clause (there’s an explicit one in California) secure a right to marry, which extends to same-sex marriages as well as opposite-sex marriages. The limit of marriage to opposite-sex couples thus must be reviewed under strict scrutiny (i.e., must be narrowly tailored to a compelling state interest).
2. The California Constitution’s Equal Protection Clause treats sexual orientation as a suspect classification. Any discrimination against gays and lesbians thus must be reviewed under strict scrutiny, and the opposite-sex-only rule is indeed such a discrimination.
3. The opposite-sex-marriage-only rule does not constitute presumptively impermissible sex discrimination, only sexual orientation discrimination.
4. The ban on same-sex marriage can’t pass muster under strict scrutiny (pretty much a foregone conclusion, given how demanding strict scrutiny generally is).
The Dish 