The indomitable ZZ Top rocks Musikfest, 7:30 p.m. Aug. 12, Sands Steel Stage, PNC Plaza, SteelStacks, Bethlehem.

The legendary Texas trio brings its hard-rock blues sound to the Lehigh Valley to perform classic hits such as "Legs," "Sharp Dressed Man" and "Gimme All Your Lovin'," as well as new material from "La Futura," its latest album, which was produced by Rick Rubin.

ZZ Top was formed in Houston, Tex., in 1969, by guitarist and lead vocalist, Billy Gibbons, bassist Dusty Hill and drummer Frank Beard.

Stemming from a roots-inspired sound, and beginning with blues-rock on its earlier albums, ZZ Top later incorporated new wave, punk and dance rock, with heavy use of synthesizers.

ZZ Top has been praised for its technical mastery and has sold tens of millions of records. The group's discography includes 23 albums. The group has garnered 11 gold records, and seven platinum.

The 1983 album, "Eliminator," remains the group's most commercially successful record, selling more than 10 million. ZZ Top was inducted into the Rock and Roll Hall of Fame in 2004. "The Baddest Of ZZ Top," a greatest hits CD, was released in 2014.

"In essence, today's ZZ Top sound is a reflection of what we've always been," says Gibbons in an email interview. "Same three guys, same three chords. It's something that continues to evolve and devolve, a paradox of a kind. We've popped out of a cosmic vortex."

ZZ Top is one of the only bands in history to have the same lineup for five decades. "It's not so much an achievement as keepin' on keepin' on," says Gibbons.

"We actually like doing this: recording, touring, rockin' it up big time. It's all something we really like doing. We're having a good time and that, for a fact, is what keeps it going."

The band's deep-rooted friendship, respect and camaraderie is key, he adds.

"We're faultlessly mindful of each other's space and at the same time we've been known to gravitate to each other when the road threads its way. Why not? It's really the essence when you think about it."

The group was a phenomenal international act in the 1970s and in the 1980s, a darling of the MTV music video era. Their stylish look and famed vehicles were the stuff of music video legend.

"Those were great moments as were the times," says Gibbons. "We certainly retain fond recollections of those visionary pieces of cinematic artistry.

"Of course, we're talking about the '33 Ford Eliminator three-window coupe," says Gibbons. "The car's still with us so, in a way, we still have that as a very real outlet. And some other cars, too."

Have the front men of ZZ Top ever considered ditching their iconic beards (which appeared during a hiatus in the late '70's)?

"It's true about the inaugural collective debut of our facial hair being serendipitous," says Gibbons. "Nothing was planned by us, but when we reconnected after a lengthy layover the whiskers had sprouted in a very real way. We just went with the flow thereafter.

"We've been offered a considerable sum to alter the overall wooly look, but it just doesn't seem worthwhile until mirrors and other reflective surfaces are outlawed."

When asked what Gibbons attributes ZZ Top's longevity and appeal to fans across several generations, he says, "It's no secret that we're very much rooted in the blues, so there's the commonality with the pulse of humankind and the pulse of the blues.

"It's downright biological and who among us is willing to deny biology? Without it we wouldn't even be here, which is really the point."