Thirty years ago this month—on May 11, 1971, to be exact—Dallas restaurateur Mariano Martinez, Jr., opened the spigot of a converted soft-serve ice cream machine and filled a glass with a history-making pale green slush—the world’s first mass-produced frozen margarita. Do not misunderstand: The beverage that emerged from the device was not the first frozen margarita ever; the drink had been around since the blender was introduced in the late thirties. No, this naughty cocktail was much more important. This was the party in a tank that fueled the disco era in Texas, jump-started the national Mexican food craze, and raised the status of tequila from a pariah to a prince among alcoholic beverages. Three decades later the stainless-steel appliance that launched a zillion hangovers sits just inside the front door of Mariano’s Mexican Cuisine on Greenville Avenue in North Dallas. It may have all the glamour of an iced-tea dispenser, but this is the machine that created the national drink of Texas. It is hard to imagine today, but in the late fifties, when Martinez was a teenager waiting tables at El Charro, his father’s Mexican restaurant in Dallas, tequila was unknown to most people in the United States and considered weird by the rest. Flipping through a scrapbook recently in his home office in the city’s affluent Lakewood neighborhood, Martinez remembers those long-ago days: “Customers—they were all Anglos—would show up with a bottle of tequila someone had brought them from Mexico and ask my dad, ‘What do we do with this?'” The elder Martinez would whip up a batch of frozen margaritas using a recipe he had gotten from a bartender at a private club in San Antonio in the late thirties. Made with fresh-squeezed lime juice, Cointreau, and a secret ingredient, the drinks were quite a hit. “The next thing you knew,” Martinez remembers, “the bottle would be empty and the people would be having a great time.”

In 1971, after a ten-year stretch during which he dropped out of high school, played in a rock and roll band, raised considerable hell, and ultimately graduated from Dallas’ El Centro College, the 26-year-old Martinez decided to open his own Mexican restaurant. “I went to my father,” he says, “and asked him if he would give me his special margarita recipe.” His dad agreed. “Papa was a hardheaded person, a private person,” Martinez says, “and it touched me that he was willing to share it. It brought tears to my eyes.” The restaurant opened in April and, thanks to word of mouth and some well-placed free plugs from the gregarious young owner’s friends in the broadcast media, it was immediately packed. On the second night, a customer stopped Martinez and asked, “Do you know how to make frozen margaritas?” “Oh, yes, sir, the best,” he answered. “Well,” the customer growled, “you’d better talk to your bartender, because these are terrible.”

Martinez says he went weak in the knees, envisioning imminent failure and the added humiliation of screwing up his father’s recipe. It was easy to see what was wrong, though. The bartender was so swamped with orders that he was just throwing ingredients into the blender without measuring them. And he wasn’t happy about having to make such a complicated cocktail. When Martinez tried to talk to the man, he blew up and threatened to walk out: “I’m going back to Steak and Ale,” he said, “where the customers only want bourbon and Coke or scotch and water.”

The next morning on his way to work, a chastened Martinez stopped at a 7-Eleven to buy chewing gum. While he was waiting in line, he noticed some kids ordering Slurpees. Suddenly, out of nowhere, a notion hit him. “It was like I was channeling the idea,” he says. “I thought, ‘We could premix the margaritas in a Slurpee machine and all the bartender would have to do is pull the lever.'” As soon as he could get to a phone, he called the Southland Corporation, the Dallas-based owner of 7-Eleven, and asked if he could buy a machine. The company representative was suspicious. “No deal,” he said. Martinez kept calling around until someone finally told him about a local man named Frank Adams who had been pestering restaurants with a crazy idea for making frozen daiquiris in a machine.

The two met and decided to pool their knowledge. Adams got hold of a soft-serve ice cream machine and started tinkering. Martinez worked on the margarita recipe. It took some experimentation to adjust for large quantities and the fact that the machine did not use ice but water (which it then froze together with all the other ingredients). A couple of weeks later they lugged the contraption into the bar at Mariano’s. Because he had nowhere to hide it, Martinez put the clunky machine out in full view. As it turned out, his customers loved the margaritas that poured out in a slithery frozen stream.

In retrospect Martinez’s timing couldn’t have been better. In a matter of months the Texas Legislature made it legal for restaurants to sell liquor by the drink in their dining rooms instead of in separate “private clubs,” and restaurants all over the state started serving cocktails. The combination of booze and a booming economy started the good times rolling, and they didn’t slow down for almost ten years. The upper part of Greenville Avenue, centering on the Old Town shopping center, became the singles destination in Dallas, and Mariano’s bar was happy-hour central. Pictures on the wall show Willie Nelson, Frank Sinatra, Jr., assorted Dallas Cowboys, and the stars of the television series Dallas (scenes for the show were filmed there on five occasions). Southern Methodist University’s party-hearty contingent practically moved into the cantina. When Bob Hope performed at SMU in the late seventies, he knew how to win over the audience. “I went over to Mariano’s for a margarita,” he told the crowd. Everybody cheered and whistled. “I won’t say how big it was,” he continued, “but the glass had a diving board.” The students shrieked with laughter. “And,” Hope concluded, “they had to put the salt on with a paint roller.”

Mariano’s was margaritaville, and its publicity-savvy owner, who sported a mustache and goatee and was given to appearing at public functions like charity events wearing a Mexican bandido outfit, became quite the local celebrity. The economic and public-relations value of his creation did not go unnoticed either. Other restaurants and clubs quickly copied his idea, and by the end of the seventies, the drink machine was required equipment in any big bar. In 1984 Martinez received a commendation from the Association of Tequila Producers (a now-defunct trade group) for putting tequila on the map in the United States. In 1996, on the twenty-fifth anniversary of the invention of the machine, both the City of Dallas and the Texas House of Representatives passed resolutions of appreciation. Martinez estimates that in the first year, when the concoction was still a novelty, nine out of ten drinks he sold were margaritas.

Martinez never tried to patent his innovation. “I was too busy running the restaurant,” he says, “and at the time, it didn’t seem like that big a deal.” His associate Frank Adams developed a nice little business leasing frozen-drink machines for a while, but once the initial collaboration was over, the two went their separate ways. (The last Martinez heard, Adams was living in Florida.) Late in 1971, after combating continual problems with the margaritas’ consistency and discovering that some of his bartenders were selling the recipe behind his back, Martinez had a commercial drink-mix company come up with a formula. That way the recipe would remain secret and there would be no variation from batch to batch. The formula makes concessions to mass production, using high-quality lemon and lime concentrates and corn syrup, common in the soft-drink business because it is cheaper than cane sugar. In the restaurant the bottled liquid is mixed with Cuervo Gold Especial tequila, Cointreau, and his dad’s secret ingredient, of course. (The top-shelf or “Texas margarita” also has Grand Marnier.) I tried one of these babies the other day, and I have to say that while it may not be a handcrafted margarita with freshly squeezed Mexican-lime juice, it had a clean, pleasant taste and it went down real smooth.

This month Martinez will celebrate the thirtieth anniversary of his creation with a margaritafest at his six Dallas-area restaurants—three Mariano’s and three La Hacienda Ranches. If you order a frozen margarita between May 5 and 11, your first drink will be the same size and price it was in 1971—six ounces for $1.25. It will not, however, emerge from a dinky, 1971-era dispenser. At the huge La Hacienda Ranch in Colleyville, for instance, three flavors (original, strawberry, and Texas) will be dispensed from four ever-churning tanks. The tanks will never run out because they will be continuously refilled by hoses leading from twenty-gallon containers of margarita mix discreetly hidden in a walk-in cooler.

No doubt plenty of people will show up for the event, and no doubt plenty of them will remember the old days, when the customers at Mariano’s on Greenville Avenue wore miniskirts and leisure suits, the cocktail waitresses wore hot pants, and—when the mood and the margs were just right—the musicians in the cantina would coax the revelers to their feet and everybody would snake-dance out the front door, disappearing into the margaritaville night.