For ZZ Top, the death of Dallas-raised bassist Dusty Hill last July spelled the end of the longest-running rock lineup of all time.

It could have derailed the band entirely. Instead, it ushered in a strange new model: ZZ Top, Mach II.

The bearded ambassadors of the blues are carrying on with a new bass player — their longtime guitar tech Elwood Francis, who now sports billowing facial hair to match the whiskers of singer-guitarist Billy Gibbons. Their first tour with Francis arrives Sept. 24 at Dos Equis Pavilion, mere blocks from where Hill grew up.

Yet even as it rolls into the future, ZZ Top is tipping its hat to the past with RAW, the last full album recorded with Hill. Released Friday, the record captures the original trio performing in 2019 in all its greasy blues-rock glory inside an empty Gruene Hall in the Texas Hill Country.

For three grizzled geezers like ZZ Top, the wooden honky-tonk built in 1887 was the perfect place to snort and strut through old gems like “Gimme All Your Lovin’” and “La Grange.”

“Over the years, every speck of sawdust has settled into that place to make it resonate like a giant speaker box,” Gibbons says. “What a great spot to record an album.”

Not that they realized tape was about to roll. Gibbons, Hill and drummer Frank Beard — the sole member sans beard — had assembled at Gruene Hall for what they thought was an interview for That Little Ol’ Band From Texas, a documentary chronicling the trio’s 50 years together.

But the film’s director, Sam Dunn, had different plans. He secretly asked the road crew to set up ZZ Top’s instruments, amps and recording gear.

“Once we realized we were ready to go, we simply strapped up and started playing,” Gibbons says. “The setting was akin to all those places we played in the beginning.”

The beginning of ZZ Top starts in Dallas-Fort Worth with Irving-based Beard and Hill, an East Dallas native who’d quit Woodrow Wilson High School to pursue music. The two teens crossed paths in 1966 at the Cellar in Fort Worth, a strip club and music joint that also had a location in downtown Dallas.

“One night, I was playing the Cellar with one group and Frank was playing with another, and my brother Rocky saw Frank and says, ‘Let’s try to steal that drummer for our group,’” Hill told me in 2008 for a story in The Dallas Morning News.

Beard joined the Hill brothers for a series of Dallas bands, including American Blues, whose members took their name quite literally: They all dyed their hair a shade of shocking blue.

Meanwhile in Houston, a teenage Gibbons was perfecting the rough-and-tumble style that would one day place him in the pantheon of rock’s greatest guitarists.

In early 1969, his band the Moving Sidewalks had landed four gigs opening for the Jimi Hendrix Experience, including a Dallas show at Fair Park Music Hall. With 40 minutes to kill, Gibbons and his bandmates padded their set with “Purple Haze” and “Foxey Lady,” a major no-no in the protocols of concert etiquette: Opening acts are never supposed to perform the headliner’s songs.

When Gibbons glanced toward the side of the stage, he spotted Hendrix standing with his arms folded, grinning.

“He grabbed me coming off stage and said: ‘Just a second. You’ve got a lot of nerve. I like that. I want to get to know you,’” Gibbons recalls. “It endeared us to Jimi Hendrix right off the bat.”

But as Gibbons’ profile grew, Hill and Beard were struggling. Unbeknownst to each other, the two ex-bandmates had both moved to Houston seeking greener pastures.

“Frank strolls into this blues-folk club I was working at and says, ‘Man, you’ve got to get together with this guitar player I know,’” Hill told The News in 2008.

The guitarist, of course, was Billy Gibbons, who’d recently lost several bandmates to the Vietnam War draft. Within months, ZZ Top was formed and headed to Tyler, where it cut its first two albums at Robin Hood Studio, a small residential home and recording complex.

ZZ Top’s First Album (1971) and Rio Grande Mud (1972) didn’t garner much attention nationally. But the third time was the charm.

Released in 1973, Tres Hombres spawned the FM staples “Waitin’ for the Bus,” “Jesus Just Left Chicago,” and “La Grange,” an ode to the long-running Chicken Ranch bordello near the tiny town of La Grange, between Houston and Austin.

Not only was “La Grange” the band’s first hit, it set off a chain reaction across pop culture. Weeks after the song came out, a Houston TV news station ran a weeklong exposé on the Chicken Ranch brothel, causing it to shut down and paving the way for the Broadway musical and film The Best Little Whorehouse in Texas.

Meanwhile, the trio set off on its marathon “Worldwide Texas Tour,” sharing a Texas-shaped stage with live rattlesnakes and a longhorn steer. While most of its fans associated the three musicians with Houston, the city where the band formed, Hill wanted people to remember its Big D roots, too.

“I’ve been bad, I’ve been good / Dallas, Texas, Hollywood,” he sang in the 1975 hit “Tush.”

As the trio’s fame grew, Hill returned to Dallas in the late ’70s seeking refuge. While Beard struggled with heroin addiction, sending ZZ Top into a hiatus, Hill worked incognito for several months at DFW International Airport.

“I just wanted to feel normal,” Hill told Ultimate Classic Rock in 2019. “We were well-known, but I had a short beard, regular length, and if you take off the hat and shades and wear work clothes and put ‘Joe’ on my work shirt ... it’s not that hard to pass yourself off.”

By the early ’80s, Beard was sober, the beards had grown longer and ZZ Top was busy expanding its sound. Gibbons was so jazzed by seeing punk rockers perform in London, he began to experiment with the style in songs like “Tube Snake Boogie.”

“I think the best word is ‘freshness,’“ Gibbons says, speaking by phone from someplace in Arizona — he’s not sure where — as he waits for his tour bus driver to return to duty.

“Punk was still rock ’n’ roll, but there was an unexpected attitude I found quite uplifting. There was no way we weren’t going to be influenced by it.”

As punk begat new wave, ZZ Top became superstars after adding synthesizers to 1983’s Eliminator album, which produced the hits “Legs,” “Sharp Dressed Man” and “Gimme All Your Lovin’.” A trilogy of funny MTV videos directed by Tim Newman (singer Randy’s cousin) established the trio as bizarre cartoon-like characters, zipping around in a 1930s hot rod emblazoned with the band’s logo.

“Someone once said ‘ZZ Top is the Howard Hughes of the blues.’ I think we can go with that,” Gibbons says.

The band eventually got rid of the synths and returned to basic blues-rock. But it was too late. A lot of people had already dismissed ZZ Top as all beard and no backbone.

The band has still never won a Grammy and is MIA on the current Rolling Stone list of “The 500 Greatest Albums of All-Time.”

If any of that bothers Gibbons, he doesn’t admit it.

“These wacky beards and crazy hats and whatnot have become a trademark, but it’s steeped in a tradition of seriousness,” he says. “When it comes to the music, it’s always been nose-to-the-grindstone.”

Those who criticize the band for appropriating Black blues music are also, in his mind, missing the point.

“The best way to describe ZZ Top is we’re interpreters of a great American art form.”

Master interpreters, according to some: “You’d heard this English version of blues that was kind of pop, but when ZZ Top hit, it was like the curtain was removed,” fellow Texan and Woodrow Wilson alumnus Steve Miller says in the documentary.

During the pandemic, Gibbons, Beard and Hill recorded songs for a new studio album they hoped would be their first in nearly a decade. But Hill had been suffering from a string of illnesses, including hepatitis C, bursitis and a hip injury that caused him to leave the group’s 50th anniversary tour last July.

Weeks later, he died at his home in Houston, of undisclosed causes. He was 72.

“He was a great performer and great friend,” says Gibbons. “And from my vantage point, he was also a man of wisdom. When he went to his physician to get to the bottom of why he was not 100 percent, he issued the edict that ‘If I’m late coming back, make sure Elwood lays hands on my guitar.’”

Days after Hill’s death, ZZ Top was back onstage with Elwood Francis on bass — a rapid move that shocked many fans, although Gibbons says it’s exactly what Hill requested. Out of respect for the late bassist, the new lineup stopped performing “Tush,” Dusty’s signature song as lead singer.

“Remarkably, Elwood didn’t miss a note,” Gibbons says. “Not only is he a dear family member, having been on deck with us for three decades [as a guitar technician], he’s also an astute player with a soulfulness that comes through loud and clear. And off we go.”

That Little Ol’ Band From Texas — available on several streaming outlets — runs just 90 minutes and ends in the mid-1980s as the band explodes into the mainstream. As this new chapter of ZZ Top kicks into gear, now could be the perfect time for a sequel, Gibbons says.

“Every story must have an end, but after five decades, ZZ Top is still rocking,” he says. “The story continues.”

Thor Christensen is a Dallas freelance writer and former pop music critic for The Dallas Morning News.