The last clause is due to a potential ballot initiative that would change California's constitution, forbidding same-sex marriage. The Chron article explains the relevant history:
Gov. Arnold Schwarzenegger has twice vetoed same-sex marriage bills, citing a ballot initiative approved by more than 60 percent of the state's voters in 2000 that reaffirmed California's opposite-sex-only marriage law. That initiative was not a constitutional amendment, which requires more signatures to qualify for the ballot.
I believe a constitutional amendment in California also requires a 2/3 majority. Given that attitudes towards same-sex marriage have moved steadily left across the country over the past decade and the fact that a less radical law could only muster 60 percent of the voters, I'm pretty optimistic about this ballot initiative failing.
Lawyerly types can get the opinion here, In re Marriage Cases, S147999, available in both PDF and DOC formats.
We now return to your regularly-scheduled blog silence.