40 years ago: From left to right: Steve Wesson, Butch Hancock, Jimmie Dale Gilmore, Tony Pearson, Joe Ely. (Butch Hancock.)

How does a band make it to the point where it can celebrate 40 years together? If you’re the Flatlanders, you do it by spending most of those 40 years apart.

The group’s core members — singer-songwriters Joe Ely, Jimmie Dale Gilmore and Butch Hancock — met ages ago in their home town of Lubbock, Tex. Music lovers with wildly divergent tastes, they hung out, moved into a house together, and eventually formed a band, playing music that borrowed from country, rock, folk and bluegrass and splashing it all with modern, often trippy brush strokes. In a sense, they were Americana before Americana was cool (or, for that matter, before Americana was a music genre).

The band lasted less than a year — just long enough to write a bunch of songs and record an album in Nashville in 1972 that was promptly forgotten. Saying it barely made a mark would be overstating its impact.

Ely left Lubbock to hop boxcars to New England, where he hoped to watch the leaves turn color (well, it was the ’70s). Gilmore departed for Denver, where he would study Eastern religions and philosophy (again, the ’70s). And Hancock moved to Clarendon, Tex., to drive tractors and help his friend build an amphitheater.

The three remained close friends, but the band was over. And the band might have remained over if it weren’t for a little thing called fate — and Elvis Costello.

The Flatlanders, from left to right: Butch Hancock, Joe Ely, Jimmie Dale Gilmore. (Steve Gullick)

Ely, reached by phone last week in Chicago, one of the first stops on an anniversary tour that brings the group to the Birchmere on Friday, tells the story.

In the ’70s, he, Gilmore and Hancock were all enjoying successful individual careers. Ely formed a honky-tonk band, toured often and even opened for the Clash, with whom he’d become pals. A full 10 years after the Flatlanders’ Nashville recording session, Costello’s record label got wind of the long-forgotten album and obtained the rights to release it in Europe.

The record took off overseas, but it would be another 10 years before its release in the United States. When Rounder released “More a Legend Than a Band,” in 1991, it essentially offered up a 20-year-old album as the group’s American debut. And what a debut: With such songs as the withering “Dallas,” the heartbroken “Tonight I Think I’m Gonna Go Downtown,” and the wonderfully wordy “You’ve Never Seen Me Cry” it delivered country that was twangier and thinkier (and weirder) than anything else out there.

The success may have been a long time coming, but the delay never bothered the guys, Ely says. “The key is to have incredible patience and no ambition, he says, laughing. “We’ve always joked that between the three of us, we have less than a thimbleful of ambition.”

Indeed, there’s a let-it-be-ness to the Flatlanders that almost defines the group.

“For one thing,” Ely says, “we never thought of ourselves as a band. We just thought of ourselves, and still do, as close friends. Every few years or so, we get together and either write some songs or go out and do a little tour. It’s probably what’s kept it fresh for us.”

In addition to celebrating a four-decades anniversary, the band is excited about releasing a new album later this summer. Well, it’s newness is relative. These songs are also 40 years old: A long-lost tape the group recorded as a demo in an Odessa, Tex., studio was recently discovered in a Lubbock closet. In August, New West Records will release the recordings as an album, “The Odessa Tapes.

“We remembered recording this, but we didn’t think the tape existed,” Ely says. “We were completely shocked because it didn’t seem possible for it to have survived and been in such good condition after sitting in the exact same spot for so long.”

Even on this earliest recording, so much of what would later be identifiable as the band’s signature sound and feel is present. Gilmore’s nasal, almost otherworldy twang, Ely’s grit and gusto, and Hancock’s literary flair and fondness for wordplay combine in songs that are satisfyingly simple yet layered with meaning and emotion.

“Butch and Jimmie were writing songs before I was,” Ely says. “I was completely fascinated by their songs. They wrote about West Texas, and there’s not much to write about there — the sky, the horizon and dirt — and then they added sort of a cosmic element that made the songs in­cred­ibly personal but universal at the same time. And I had never encountered songs like that, and they quickly became my favorite songwriters.”

What Ely also realized is that in the case of the Flatlanders, the sum was greater than — or at least markedly different from — its parts.

“There are certain songs we write that we realize could never have been written by any of us individually, because there’s so many different influences,” Ely says. “There’s music that I like that Butch and Jimmie just can’t stand. It’s this amazing thing of liking to play music altogether but not necessarily having any of the same tastes in anything else. I think that makes it a unique combination.”

Since that long-lost first album, the Flatlanders have managed to make up for some lost time, releasing three albums of new material in the past decade. But the force that drives them is creative, not commercial.

“We’ve never tried to go out and conquer the world,” Ely says. “It’s just an immense pleasure, especially in these last 10 years, putting songs together from the ground up. It’s a real kind of excitement to see what comes up and comes out.”

The Flatlanders perform at the Birchmere, 3701 Mount Vernon Ave., Alexandria, Friday, June 29, at 7:30 p.m. www.birchmere.com. Their album, “The Odessa Tapes,” will be released Aug. 28 on New West Records.