A generation has passed since the terrorist attacks of Sept. 11, 2001.

Almost a quarter century.

I can’t decide which measurement seems to me longer, which one demonstrates more dramatically the passage of time since that terrible, unforgettable morning.

Here’s another: No one younger than 27 or so is likely to have any distinct memory of the event.

And to remember it with anything like the perspective of an adult, you’d have to be, today, around 40 or older.

On that day I was less than two weeks shy of my 31st birthday, an age that seems improbably distant.

This of course is the great mystery of time.

Our memories do not depend solely on chronology.

An event that happened 23 years ago isn’t necessarily murkier than an episode that happened a decade later, or more clear than one a decade older.

How old we were at the time matters a great deal.

Also where we were when we heard what happened.

And what we were doing at that moment.

Our brains, miraculous processors and repositories of information that they are, can’t be considered reliable on all matters, to be sure.

A great deal of research has shown that our recollections, even of very recent events, are quite fallible.

The eyewitness beloved of fictional stories of crime, whose precise testimony puts the foul killer in prison for life, does not as a rule exist in reality.

Some of the episodes we remember did not happen exactly as our memories insist they did.

I am confident about parts of my experience on the morning of Sept. 11, 2001, only because I have written documentation.

I can leaf through a bound volume of Baker City Herald issues and read the story I wrote after interviewing people at the Baker Truck Corral and along East Campbell Street near the freeway.

I remember those conversations, but only vaguely.

I know I talked to a man who was working on his pickup truck, parked on the north side of Campbell Street, but if my story hadn’t been published I would have been hopeless to remember either the man’s name, where he was from, or the nature of the mechanical malady.

(His name is Wade Hamilton, he was from Boise, and his friend was installing a thermostat in the truck. These details are preserved in ink and in pixels (the Herald had not long before launched its website) but are absent from my memory.)

But I’m not certain about other details.

I believe that I was at home when I saw on TV footage from Manhattan showing the first jet crashing into the North Tower, and that I was in the conference room at the Herald’s former office, on First Street between Washington and Court avenues, when the second plane crashed.

But it’s possible, given the sequence of events, that I watched both at the office.

I will never know for sure.

And of course it doesn’t matter.

Yet the absence of certainty bothers me just the same.

It seems to me that for an event as significant as Sept. 11, 2001, I ought to be able to be recall with crystalline clarity even the details that on any other day would be mundane, which is to say eminently forgettable.

I should remember the color of Hamilton’s pickup truck, whether it was a Ford or a Chevy or a Dodge.

One color I do recall is blue.

The deep blue of the sky over Manhattan on that late summer morning, as I watched the TV coverage, seemed to me the same shade that I saw when I looked outside at the Elkhorns, their sharp peaks appearing to be etched against that azure backdrop.

There was one difference, though, between what I saw on TV and what I saw when I walked outside.

Smoke.