But despite their differences – or perhaps because of them – Calexico (a Tucson, Ariz. band that mixes rock riffs with Mariachi rhythms) and Iron & Wine (a group that’s essentially singer-songwriter Samuel Beam) have formed one of this year’s most interesting collaborations.

Playing packed shows across the country in moderately sized venues, the two groups have led a tour, soon to conclude, of indie rock cross-pollination, inviting guests along the way in the style of Bob Dylan‘s famed 1975 Rolling Thunder Revue tour or The Band’s collaborative Last Waltz concert.

In New York, banjo-playing Sufjan Stevens came aboard. In Los Angeles, it was bassist Mike Watt, formerly of the `80s post-punk band the Minutemen. James Mercer from The Shins came along in Portland, Ore.

“We try to invite guests out to make the show that much more special, to get outside of your own path,” says Joey Burns, Calexico frontman.

The collaboration began with In the Reins, a seven-song album released earlier this year by Calexico and Iron & Wine, featuring songs written by Beam and played with Calexico arrangements.

Describing his musical tastes, Beam frames the overarching theme of their venture: “There’s a lot of music out there.”

A Florida native, the bearded Beam – more amusing and mischievous than his songs would suggest – worked as a film instructor in the late `90s in Miami, recording lo-fi basement tapes in his spare time. Beam has since released two critically acclaimed albums featuring his gentle whispers and acoustic strumming.

He is modest enough to only sheepishly acknowledge that he painted the watercolor cover of “In the Reins” – and doesn’t appear to be very possessive of his tunes, either. His two greatest songs, “Jezebel” and “The Trapeze Swinger,” aren’t even included on a proper album – the former on his Woman King EP earlier this year, and the latter on the soundtrack to the Dennis Quaid comedy “In Good Company.”

Founded by Burns and drummer John Convertino, Calexico has been around for nearly a decade. The group includes horns, vibraphone and steel guitar. Usually, half of its albums are instrumentals.

They’ve done session work with singers like Richard Buckner and Vic Chesnutt. But the band has grown in popularity on its own, especially since its 2003 album, “Feast of Wire.”

Burns jokes that it was an “Internet hook up” that first got the bands together. In actuality it was Howard Greynolds, the owner of Overcoat Records and a friend of both, who had the idea for the collaboration.

Originally, there was thinking that Burns and Convertino could be the backing band for Iron and Wine’s debut, but they weren’t able to get together until “In the Reins.”

“It was a very natural and innocent thing that I think I kept going (by getting them together),” Greynolds says. “We never intended to tour, but when we made the EP, everyone got on so well.”

Beam, songwriting poet, and Calexico, masters of instrumentation, turned out a good match.

“I think we all have varied musical tastes and it all kind of fits,” says Beam. “So that’s what we try to get across – it’s kind of how you define your genre of self.”

In concert, Calexico opens with a set, which segues into a few numbers from Mexican singer Salvador Duran, a south-of-the-border Pavarotti who was performing at the lobby of the Tucson hotel where Beam stayed while recording with Calexico. He ended up singing a grand, powerful verse on the album’s first track, “He Lays in the Reins.”

Iron & Wine then play a set of their own, often with cameos from members of Calexico. Finally, together they perform a set of In the Reins songs.

When the two bands first unite on stage – numbering 13 strong, including Duran – to play the sweeping “He Lays in the Reins,” the fullness of sound gives an unmistakable feeling of triumph, as if it’s the climax of a film – maybe a rock ‘n’ roll version of “Buena Vista Social Club.”

Above all, Calexico, Iron & Wine, Duran and other guests – in a musical world so divided by genre and classification – give a sense of inclusion.

Burns says the audience response has had a spark to it, and that the concerts feel special, both to the crowd and the musicians.

“The fact that there’s a community, you kind of get lost easier,” he says. “Talking to different people, going off on adventures, musically or otherwise, or trying different things with arrangements of songs.”

Clearly, the groups have affected each other. Beam has begun playing new versions of some songs, including an exciting, up-tempo arrangement of “Jezebel.” Calexico’s next album, Garden Ruin, due April 11, is the band’s most vocals-centered effort yet.

Though the North America leg of their tour is coming to a close, they will spend several months in Europe in April and May touring together. After that, surely to the disappoint of many, they have no plans to continue the collaboration.

“We approached it from the beginning as a one-off kind of thing,” Beam says. “But you never know.”

Jake Coyle / Associated Press Entertainment Writer