The April 18, 1906 earthquake that ending up killing 3,000 people and destroyed 80 percent of the city isn’t the most tectonic San Francisco event that sent shock waves across the nation.

It was a cultural edict on Feb. 12, 2004 made on the steps of San Francisco’s City Hall that unleashed a political tsunami.

Then San Francisco Mayor Gavin Newsom directed the city clerk to start issuing same-sex marriage licenses.

Newsom’s most quoted words from that day were prophetic: “The door is wide open. It’s gonna happen whether you like it or not.”

Before the door was closed by the courts on March 11, 2004, there were 4,000 same-sex couples married in San Francisco.

Four years later on Nov. 4, 2008, voters in California overwhelming passed Proposition 8.

It was dubbed the “Marriage Protection Act.”

A year later, a lower court overturned the proposition before the 9th District Court of Appeals reversed the ruling.

The United States Supreme Court refused to hear an appeal.

Then the high court’s decision in Obergefell v. Hodges in 2015 deemed barring same sex marriages was unconstitutional.

The ruling protected same-sex marriage under the Due Process and Equal Protection Clauses of the 14th Amendment.

Therefore, same-sex marriage became the default law of the land.

In less than 90 days, Californians are once again going to weigh in on the question of same-sex marriage.

They will decide the fate of Proposition 3 on the Nov. 5 ballot.

The proposition is titled, the “Right to Marry and Repeal Proposition 8 Amendment.

It was placed on the ballot with the bipartisan support of both the State Senate and State Assembly without a single vote cast in opposition.

If voters pass Proposition 3, it will purge the California constitution of language inserted when Proposition 8 was approved which defined marriage as a union between a man and a woman.

It would also declare a “right to marry is a fundamental right” of Californians.”

Failure to pass keeps the Proposition 8 language intact although it is “inoperable” unless at some point in the future another Supreme Court decision makes it once again valid.

A lot has happened in the past 20 years.

Arguably, the biggest lesson besides the fact civilization hasn’t collapsed with government sanctioned same-sex marriages involves the basic documents governing 326.7 million Americans.

The Bill of Rights is not an owner’s manual with every possible scenario and concern addressed in fine print.

It is a framework to the rights of citizens and how 326.7 million individuals can interact, keeping in mind there must be rules to sustain a society and a republic.

The overturning of Roe v. Wade was viewed by some as blasphemy and others as divine providence.

The reality in context of the American experience, it happened because Congress did not act to essentially enshrine the ruling through law in a manner that would withstand constitutional scrutiny.

The system is set up so the people can seek redress from what they perceive are unjust laws by accessing the judicial system.

Integration was set in motion not by lawmakers but the judicial system weighing in on grievances from the people in the form of lawsuits.

This, of course, set off the familiar whine from political hacks decrying “judicial activism” that implies the courts are making the laws. It’s the same song you are hearing today from politicians having coronaries over Supreme Court decisions they disagree with.

Imagine what would have happened if the president back then pushed a plan to reform the court because of a decision made ending segregation that was opposed by Congress and not widely embraced.

As an aside, it was a court led by a Republican — former California Gov. Earl Warren — appointed by President Dwight Eisenhower, another Republican.

And guess who was the target of never ending vicious attacks on the far right and even the far left: Chief Justice Earl Warren.

American society and how it is governed was never meant by the founders to be cast in rigid stone based on a course of action by those that gave birth to kingdoms or fashioned the reins and muzzles of dictatorships.

Instead, it allows movement.

As such, we get pendulum-style movements as society advances.

The courts mediate such movements, hence the symbolic scales representing a balancing act between law and justice.

Keeping Proposition 8 in place is lazy governance.

It is also dangerous.

That’s because a future judicial ruling based on circumstances never considered possible can change the course of human events as it always does.

That doesn’t assure that one day there won’t be an effort to undermine the right to marriage for a reason that we can’t even phantom today.

But what it does assure is that diluting, or even taking away that right, is much harder to do if it is enshrined in the state’s constitution.

There are those opposed to Proposition 3.

Some say the wording will open the door to siblings or cousins marrying. But that is a bit far-fetched as other laws have prevented such opposite sex and same sex marriages in California.

Most opposing likely will dislike the idea of the state intruding on a religion.

Keep in mind religions, and not governments, were the first to come up with the concept of marriage.

The secular and non-secular worlds need to co-exist.

And a long time ago the non-secular world whether it was through kings, dictatorships or another vessel recognized the need to control the masses.

That meant finding a way to co-exist with religion.

Thus marriage — or unions of individuals — became a building block for non-secular civilizations.

Even though marriage today is seen as a right controlled by government, it still has its roots in religion.

The bottom line is there will be Californians that vote against Proposition 3.

This will not mean they are evil or whatever term self-righteous types plaster on those they disagree with. They simply have a different viewpoint.

Proposition 3, though, blazes no new ground.

Credit that to San Francisco and the “Winter of Love” Gavin Newsom spurred as mayor of San Francisco.

And just like the infamous 1969 “Summer of Love” some 55 years ago, what happened in the City by the Bay has reverberated not just across the nation but the world as well.