Calexico’s sound, which falls somewhere between spaghetti Western, surf rock, mariachi, jazz and alt-country, has always been difficult to classify.

But whereas many bands of Calexico’s indie standing would push further into the obscure, Calexico moves more into the mainstream on 2006’s “Garden Ruin.”

“We wanted to show a different side to what we do,” said Calexico vocalist Joey Burns. “People tend to kind of write you off, they say, ‘Oh OK I’ve got the story.’ There’s a lot more depth to what we do.”

Adding more rock ‘n’ roll elements to “Garden Ruin,” Calexico is trying to resist being boxed in by its own distinctiveness. What results is pure alt-rock as only

Calexico could – their attempt at a more accessible sound brings four more band members into the studio and thousands more fans out to the concerts.

Calexico itself began as an answering machine message. “John (Convertino) would play some drum beats into his answering machine, he liked how it sounded recorded that way,” Burns said. “I came in to add some guitar later.” This was 1996, officially the year of band’s first recorded music.

A year later they released the album “Spoke,” which was then the title of their project – they didn’t become Calexico until after this release, when they saw a road sign for the small border town. “It just seemed to fit more to what we were doing at the time,” Burns said.

The following years brought three more full-length albums, flirting with mariachi, electronica and jazz along the way, and a live DVD in 2004. They have joined forces with artists like Neko Case, Nancy Sinatra and, maybe most importantly, Iron and Wine’s Sam Beam for the album “In the Reins” in 2005.

Naturally, their fifth album was influenced by all these factors. “(‘Garden Ruin’) was a conscious decision to try something new and tap into strains in our musical fabric that haven’t been highlighted in the past,” Burns said, pointing out a lack of an instrumental track (a first for Calexico) and the overwhelming political theme.

“We have so much built up frustration from the Bush administration,” Burns said. “Our other albums were political but not like this one.”

Radio-ready track “Cruel” reflects on environmental corruption with the lyrics “Cruel, heartless reign / chasing short-term gains Ö Birds refuse to fly / no longer trust the sky,” while the tracks “Letter to Bowie Knife” and “All Systems Red” speak of religious fundamentalism and political extremes.

These political references aren’t obvious. Burns said he prefers an expansive metaphor in his songwriting over in-your-face left-wing statements. The songs could easily be mistaken for something else, but Burns assures us “there’s monsters lurking all over it, even in the pretty bits.”

Calexico’s new sound takes advantage of those big, big landscapes they used to sing about. Except this time, they’re filling them with an equally big sound.