Let me start the official mourning.

For what was once the coolest spot in all of sports. The epicenter of winning.

The Oakland-Alameda County Coliseum complex.

With the A’s announcement that they plan to build their long-awaited ballpark at the Peralta Community College site, the abandonment plans are complete.

Nobody intends to stay at the intersection of Interstate 880, Hegenberger and 66th Avenue, the site of the most championships in Bay Area sports history.

First, the Golden State Warriors — who won three championships while residents of the Coliseum complex — announced their plans to move back to their first Bay Area home, San Francisco, by 2019.

Then, the Oakland Raiders waved goodbye. Again. They christened the Coliseum in 1966, were one of the NFL’s best teams back in the day while helping make Oakland the hippest locale in the league. They twice have rewarded their loyal fans by choosing to abandon them, this time for Las Vegas sometime in the next two or three years.

And now the A’s — the franchise that has been determined to leave Oakland for years — might be on the way out. Not out of the city as its owners once wanted but 5 miles away, near downtown, Laney College and Lake Merritt.

If the Laney site comes to pass, and that’s a big if, that will leave the great concrete and asphalt slab — 121 acres in all — void of teams.

But full of memories.

For those of us old enough to remember, Oakland was where winning happened. The A’s won three straight World Series: 1972, 1973 and 1974. In 1975, the Warriors got into the mix, winning their first NBA championship in the Bay Area. The Warriors passed the baton to the Raiders, who — after knocking on the door for most of the late 1960s and early 1970s — finally won a Super Bowl after the 1976 season

What is hip, as Oakland’s Tower of Power used to ask? The Oakland Coliseum complex was.

That was the height of the site’s powers. And even though the complex has been maligned, shunned and ridiculed in recent decades, it actually has continued to produce winners. The A’s went back to three World Series in the late 1980s and early 1990s. The Raiders were resurgent in the early 2000s and are again now.

And the Warriors have proven that you still can mine excellence at the hardscrabble corner of Hegenberger and 880.

This isn’t a treatise on the pluses and minuses of new sites or modern buildings or entirely different cities. Or on the poor decisions that Oakland and Alameda politicians made over the years. Or the combined folly of the ownership of the three tenants in so many different instances.

It’s not even a commentary on the fact that after competing with each other for exclusive rights to the site for so many years, it is the height of absurdity that both the Raiders and A’s are choosing to abandon it.

Nor is this a remark on the wastefulness of abandoning an existing site for shiny new places where the accessibility, comfort level and success of the teams are only theoretical at this point and might prove to cause more problems. (Oh, hey, Levi’s Stadium.)

This is simply the start of a mourning process for a huge, centrally located, easy-to-access site.

That produced some of the greatest sports moments that not only the Bay Area, but the world, has ever seen.

Ann Killion is a San Francisco Chronicle columnist. Email: akillion@sfchronicle.com Twitter: @annkillion