California Proposition 8 (ban on gay marriage)
has been struck down in
federal district court as a violation of the US Constitution's Equal Protection clause.
This is the first time a state ban on gay marriage has been challenged in federal court. It is worth noting that the judge is a Republican and was appointed by Reagan.
It will now go to the
9th Circuit Court of Appeals, which is also in San Francisco. If the circuit court rules for gay marriage, it will also become legal in Alaska, Arizona, Hawaii, Idaho, Montana, Nevada, Oregon, Washington, Guam, and the Mariana Islands.
Regardless of the 9th Circuit's ruling, it will be appealed to the
US Supreme Court (SCOTUS). If the 9th Circuit rules for gay marriage, SCOTUS
must hear the case because of the fracture along state lines.
If the 9th circuit upholds the ban on gay marriage, SCOTUS can simply refuse to hear the case, effectively upholding the ban. Or they can agree to hear the case and make their own ruling, which will then apply to every state in the union.