There’s one aspect of the California marriage decision that’s almost as important as the outcome: the legal reasoning the court used in reaching its result. The opinion contains great news for gays and lesbians in California — and perhaps elsewhere — that goes beyond marriage.

The California Supreme Court didn’t just state yesterday that marriage is a fundamental right open to gay and lesbian couples. It also became the first high court in the nation to state that any law that discriminates against gay people will be treated with the same skepticism as laws that discriminate on the basis of race or gender. Any such laws will have to survive a heightened level of scrutiny in order not to be found unconstitutional. Not even the U.S. Supreme Court uses that heightened standard for sexual orientation discrimination.

In deciding cases involving equal protection violations, the U.S. Supreme Court uses different levels of scrutiny depending on the characteristic that is being discriminated against. Under the lowest level of scrutiny, “rational basis” scrutiny, a government entity merely has to show that the discrimination is rationally related to a legitimate government interest. The classic case comes from the 1950s, in which the Court upheld an Oklahoma law stating that optometrists were allowed to replace lenses but opticians were not. The Court found that the state legislature could have put forth a rational reason for the law.

The Court uses higher levels of scrutiny in evaluating laws that discriminate against certain groups. While the criteria seems flexible, these are generally groups that have a long history of suffering from discrimination. The most common are racial minorities and women. But the Supreme Court has never stated that gays and lesbians deserve the same heightened protection. Even when it’s struck down laws that discriminate against gays — such as the sodomy laws and the Colorado constitutional amendment that outlawed any laws that bar gay discrimination — the Court used rational basis scrutiny, finding that there was no rational reason for these laws.

In interpreting their own state constitutions, state supreme courts tend to follow the lead of the U.S. Supreme Court. State constitutions can’t provide fewer rights than the U.S. Constitution does. But since constitutional rights are a floor and not a ceiling, state constitutions are free to grant more rights than the U.S. Constitution does. To my knowledge, and to the knowledge of most commentators I’ve read since yesterday, until yesterday no state supreme court had treated sexual orientation as a suspect classification in a law. But now the California Supreme Court – allegedly the most influential state court in the nation — has done so.

Even if the proposed constitutional amendment restricting marriage to opposite-sex couples passes in November, that ruling will stand. (Except in the area of marriage, of course.) And perhaps other state supreme courts will eventually follow California’s lead.