It is well past midnight, and a weary journalist is walking in the dark along a road across the river from central Culiacan in the Mexican state of Sinaloa.

He is a lone gringo in one of Mexico's most notorious and active drug-trafficking regions. A police car pulls over, and two cops begin grilling him, asking for his ID and demanding to know where he's been, where he's going and where he will be staying.

Instead of a south-of-the-border equivalent of a scene out of "Midnight Express," the situation resolves with our protagonist, Elijah Wald, seated between the cops, "trying not to jostle their submachine guns" as they drive him back to his hotel.

Wald had just left a concert in the Carta Blanca baseball stadium. The headliners were Los Tucanes de Tijuana, one of the top groups in norteno, the Mexican country music that has skyrocketed in popularity in the U.S. and Central America over the past decade or so. Wald -- a Massachusetts-bred former music critic for the Boston Globe, Sing Out! and Living Blues; the author of "Josh White: Society Blues"; and a recent Grammy winner for his liner notes to the Arhoolie Records 40th Anniversary Collection: 1960-2000 -- was about halfway through his research travels for a book about the "gangsta polka" music known as narcocorrido. Played in simple polka or waltz time by traditional accordion-and-guitar combos, sometimes juiced up by a full brass band (banda), these flamboyant story songs catapulted Los Tucanes, Los Tigres del Norte and other bands to stardom and became a full-fledged craze after the 1994 murder of pop sensation Chalino Sanchez.

Grasping the writer's mission, one of the cops passes Wald a notebook full of his own song lyrics. "I have plenty of songs much better than Los Tucanes'," the cop tells him. "It's just that I don't have their connections."

Since none of the songs were corridos, that's where the cop's story ends in "Narcocorrido: A Journey into the Music of Drugs, Guns and Guerrillas." But Wald's book, published last November by Rayo/HarperCollins, is rife with similar little adventures as the author hitchhikes through Mexico and the U.S. Southwest and scours the barrios of Los Angeles, seeking out and interviewing the corridistas -- the heretofore unheralded songwriters behind these phenomenally popular musical narratives.

Wald, in the midst of a promotional book tour that makes three Bay Area stops May 7-10, says he rarely found himself in threatening situations while hitching rides from truck drivers up into small towns in the Sierra in search of the composer of one classic corrido or another. "I was regularly warned by people from other parts of the country that in Culiacan I would be in danger," he writes. "They would point out the near-daily news items about killings in the city or its suburbs, many of them professional hits obviously related to the drug traffic."

But Wald, who had first journeyed to Mexico in 1987 and returned in 1995 as a peace observer in Chiapas, felt safe during his year-long travels in 1999. "For a white guy in a Third World country, there's no place safer than standing on the side of the road with your thumb out," he explained in a phone interview from Phoenix last week. "You're wearing a big sign saying, 'I don't have anything worth stealing.' I wasn't investigating the drug world, I was investigating the mythology. I was not asking questions like, 'Who killed Chalino Sanchez?' or, 'So, where do the real drug traffickers live here in town?'"

He had been fascinated with the corrido tradition ever since hearing a ballad about tequila smugglers, sung to him by a San Antonio hashish dealer in Morocco. Reviewing Los Tigres del Norte's Jefe de Jefes album for the Boston Globe further excited him about these corridos, who lionize the drug-trade outlaws.

Praising those who garner great wealth through their illegal enterprises is an ancient tradition, logically connected to the ballads of defenders of the poor and political martyrs. (Woody Guthrie's "Pretty Boy Floyd" and Bob Dylan's "John Wesley Harding" are just two examples from the U.S. folk tradition.)

In Mexico, the original corridos evolved from old Spanish ballad styles and took on their own flavor in the Texas-Mexico border region in the 19th century. They became a national phenomenon during the Mexican Revolution (1910-1920). (In 1996, Arhoolie issued a four-CD box set, The Mexican Revolution: Corridos About the Heroes and Events of 1910-1920 and Beyond!, with an entire disc devoted to songs about Francisco "Pancho" Villa.) Corridos took an interesting turn during the Prohibition era (1918-1933 in the U.S.), as songs about tequileros (tequila smugglers) entered the corrido repertoire alongside war and crime ballads.

Narcocorridos flashed into public consciousness in 1972, when Los Tigres del Norte, a Sinaloan band transplanted to San Jose, Calif., had a huge hit with "Contraband y Traicion" ("Contraband and Betrayal"). Now such songs pepper the repertoires of major norteno pop groups that fill stadiums and sell millions of records, and they provide the boom-box soundtrack to Mexican gangsta life in Lynwood, South Gate, Long Beach and other L.A. neighborhoods. They are crucial to the drug culture in Santa Fe, New Mexico, and are played as far north as Seattle.

In his research, Wald found the smoking gun that proved his contention that narcocorridos are just an extension of the earlier bootlegging corridos. A 1934 song, "El Contrabandista," written by Juan Gaytan and recorded in San Antonio, describes a smuggler going to jail after switching his business over from "champagne, tequila and Havana wine" to "cocaine, morphine and marijuana."

"Narcocorrido" palpably vibrates with similar discoveries, primarily because Wald is turning previously untilled soil. Although he hails the corrido as "one of the most vibrant and relevant art forms in the Americas," he says most educated Mexicans consider the current norteno sound "hick" music and are especially "horrified by the narcocorridos" and bemoan "the decline of a once-noble form." So when he attended the biannual International Corrido Conference in L.A., he found "absolutely nobody" studying the contemporary corrido and its composers. "How often do you have an entire pop-music scene selling millions and millions of records and no one else writing about it?" he asks. "It's every journalist's dream come true."

And when he started hunting down the composers, he found it surprisingly easy to gain access. "The songwriters are acutely aware of the fact that everybody knows their work and nobody knows them," Wald explains. "People appreciate their songs for their degree of craft, but very few people have any idea who writes the songs. But it's not so different here. How many people knew who wrote Elvis Presley's songs?"

In "Narcocorrido," Wald vividly sets the scenes in first person, sketches the historical and cultural contexts -- whether on a dusty rancho or in a Lynwood nightclub -- and then generously lets such corridistas as Paulino Vargas, Enrique Franco and Teodoro Bello tell their own (often literally rags-to-riches) stories. "To me, these guys are really important writers," Wald says. "They are among the major writers talking about life in Mexico and on this side of the border -- from a Mexican point of view -- and nobody ever treats them as serious writers."

Wald takes pains to point out, both in "Narcocorrido" and in conversation, that these narcocorridistas address a wide range of topical subjects in their songwriting, not just the glories of ill-gotten gain. "I was most surprised by the extent to which all of the writers saw themselves as inheritors of the tradition of the medieval troubadours," Wald explains. "They all insist that they are reporters, that what they do is still that tradition of being the accurate voice of what's really happening."

The newest Los Tigres album includes a corrido about Mexican president Vincente Fox, he says, with a sardonic line about celebrating progressive change with "a toast in Coca Cola." Jesus "Jesse" Armenta, for another example, wrote a brilliant muckraking song, "El Circo," about corruption in the Salinas administration. "A lot more people heard 'El Circo' than read any editorial that was ever written on the same subject, or than read Carlos Fuentes," Wald says. "But it's never treated as contemporary writing. That inspired me."

Still, the narcocorrido, despite being banned from Mexican radio and drawing howls of protest from commentators who decry its alleged promotion of the gangsta lifestyle, remains an important phenomenon, especially in the sounds coming out of Los Angeles. "I'd been making an analogy between narcocorridos and gangsta rap for some time," Wald says, "and I just found out that El Original de la Sierra, who is sort of the big star of the L.A. narcocorrido singers right now, has a hidden track on his new album that's gangsta rap in English."

Wald is amused by those, like the writer of a March 23 Los Angeles Times piece, who see the narcos as a diminishing trend. "His evidence was that he had interviewed Los Tigres and Los Tucanes and Lupio Rivera and they had all explained that it was all over," Wald says. "Everybody, once they get to be stars, moves a little bit away from that association. But call the record stores and see whether in fact narco isn't what's selling anymore. The day the Tigres go on stage and don't sing 'Contrabando y Traicion' and 'La Banda Del Carro Roja,' pigs are gonna fly."

Elijah Wald will appear Tuesday, May 7 at 7:30 pm at Black Oak Books, Berkeley; Wednesday, May 8 at 7 pm at City Lights Booksellers, SF; and Friday, May 10 at 8 pm, Mission Cultural Center, SF. For itinerary details, go here.

In conjunction with the publication of Narcocorridos , Elijah Wald and Angel M. Matos compiled a 16-track CD, Corridos Y Narcocorridos , for Fonovisa Records. It features Los Tigres Del Norte, Chalino Sanchez, Pedro Rivera, Grupo Exterminador and others. Go here for more information.