With absolutely no fanfare or fuss, one of the Bay Area’s most important 20th century structures is disappearing before our eyes: the 80-year- old eastern span of the Bay Bridge.

Next week, the last of the five biggest steel truss sections that supported two decks of traffic is scheduled to be lowered onto barges waiting below. As the vessels cart away the massive relic, workers above will continue their years-long task of taking apart the doomed visual landmark, piece by piece by piece.

“Taking the old bridge apart is as technical, or more so, as the building of the new east span” that opened in 2013, said Leah Robinson-Leach, the spokeswoman for the project that never seems to end. “There have been years of planning and collaboration.”

The engineered erasure has been visible to anyone driving past, especially with such dramatic strokes as the removal of the middle of the half-mile-long cantilevered truss that spanned the deep water near Yerba Buena Channel. The last year has been more about dematerialization than anything else — take out a truss, remove the support towers and piers below, repeat procedure — and this will be the case until the line of smaller trusses near the Oakland shore fades out sometime in 2018.

But the best view is from the bicycle and pedestrian path that lines the old span’s replacement, the wannabe icon with that single enormous cable that cradles the roadway and hangs from a single white tower. It’s a ride I make once a year to pay homage to the original — a gray steel structure that never aspired to be anything more than a direct route from point A to point B.

From that vantage point, I watched Monday as crews checked the enormous wheels that have been installed on the four corners of the truss span, thick wheels that hold spool-like strands of cable that will lift the steel frame, pivot it out and then lower it toward a pair of waiting barges (the truss will be poised between the two of them — bridging them, if you will). In recent weeks, every nonessential piece of steel has been removed from the section, which is 504 feet long and 80 feet tall. Even so, the remaining skeleton still weighs 3.2 million pounds.

Erasure of another sort could be seen at water level, where crane-size jackhammers on floating platforms pound holes into the concrete piers that held sections of the bridge that already have been removed. Into the holes will go explosives, so that the underwater portions of the piers can be imploded. The machines’ harsh clang was audible despite the traffic whizzing behind my back.

At the far end of the bike trail, beyond a sign reading “PATH CLOSED/NO TRESPASSING/STRICTLY ENFORCED,” you could look down to the shore of Yerba Buena Island and see one of the sections that still must be installed to close the 70-foot gap between the section of pathway that’s open and the final descent to the island.

I’m told there’s a decent crowd of riders up there on weekends. No doubt that also will be the case after the gap is sealed and the connection down to the island opens in what we’re told is late summer. Yet on a sunny summer weekday afternoon, congestion wasn’t an issue as I pedaled west from Oakland’s nonglamorous shore — yes, that’s a waste treatment facility on your left! I saw perhaps 12 other bicyclists in all. They’d reach the end, pause to take swigs from their water bottle and maybe snap a photo or two, and then coast briskly back to shore without stopping.

Too bad. What’s left of the original eastern span deserves a moment of contemplation or at least a discreet salute.

The structure coming down was always the poor cousin to the muscular suspension bridge that leaps with unapologetic force from the middle of the bay into San Francisco’s urban realm — now more than ever, with the residential towers of Rincon Hill pushing close. The one time the eastern span got prime attention was for the worst of reasons. One section snapped during the Loma Prieta earthquake in 1989, somehow leaving just one motorist dead.

Yet, except on that tragic occasion, the eastern span did its job, pragmatic not poetic, with an air of homely determination. Take a look at what’s there now — vertical steel, horizontal steel, diagonal steel, all in the process of being disassembled — and the practicality shines through all the more powerfully as everything not essential is removed.

Like everything else about the saga of the eastern span — 10 years late, $5 billion over budget, but, hey, at least it’s still standing — the demolition has taken unexpected turns. The cormorants, for instance. Those black waterbirds that began nesting on the old span decades ago have shown no inclination to move to custom digs on the newcomer. That netting you see on some of the smaller trusses is there to keep them out of stretches being taken apart.

“We’ve worked with environmental agencies throughout on the removal of trusses” to make them as bird-friendly as possible, Robinson-Leach said Monday. “Everything about this project is unique.”

For the record, the daylong departure of the final 504-foot-long truss is set to take place next Wednesday. But if the weather forecasts call for waves too rough or winds too brusque, it might move up or back a day. Whether you’re building a bridge or taking one down, there’s a simple rule to follow: better safe than sorry.

Place is a weekly column by John King,the San Francisco Chronicle’s urban design critic. Email: jking@sfchronicle.com Twitter: @johnkingsfchron