According to a report from the Associated Press (AP) based on interviews with the Federal Police, authorities were led to the clandestine mass graves by Sinaloa operative Bernabe Monje Silva, following his arrest in March. He is reputedly the fourth-in-command of a group known as Los M, which is closely aligned with longtime Sinaloa Cartel boss Ismael Zambada and his partner, Joaquin Guzman Loera, alias "El Chapo."

While initially overshadowed by the discovery of several mass graves in Tamaulipas, the death toll in Durango has steadily increased as the authorities have continued digging. More than 200 bodies have so far been discovered, some buried for only a few weeks and others for more than a year. According to the AP's sources, many of them were enemies of Los M.

For much of the past few years, the Zetas were Los M's principal adversaries in Durango, a northern state that contains trafficking routes to key border cities like Juarez, Reynosa, and Nuevo Laredo. However, an anonymous Federal Police source who spoke to the AP said that Los M have for the last few months been locked into a battle for control over Durango's smuggling routes with two rival groups from within the Sinaloa federation. The source identifies these groups as the Canelos and the Cabreras. This conflict is presumably responsible for a large number of the bodies in the mass graves.

The AP's report adds further information to accounts from Mexican newspaper Proceso, which reported earlier this month that the Canelos are a group of traffickers led by Abel Rodriguez Guzman, who hails from the town of Canela, Durango. Their allies, the Cabreras, are headed by Felipe Cabrera Marquez and his three brothers. Both groups have longstanding business ties to the Sinaloa bosses, but they appear to be acting on their own now. As is common among Sinaloa-connected traffickers, Rodriguez also has personal ties to the cartel’s small circle of leaders: his grandson is the nephew of Ignacio "Nacho" Coronel, who, until his death last summer, functioned as the Sinaloa’s foremost man in the Pacific region of Jalisco, Nayarit, and Colima.

However, even before the most recent revelations, there were rumblings of strife within the Sinaloan network. Over the past few months, there have been signs of discontent from Los M and the Gente Nueva, another Sinaloa subgroup associated with the organization’s ongoing fight with the Juarez Cartel in Chihuahua. Both groups have uploaded videos to the web and hung “narcomantas,” or posters, around Durango accusing Cabrera and his backer, Noel Salgueiro, of trying to move into the city. The dispute has resulted in a series of gunfights and executions around the region.

The fighting in Durango raises the question of whether the discord could spread to other regions of Sinaloa power, or even up the chain of command. The group’s unified top tier (Guzman, Zambada, and Juan Jose Ezparragoza Moreno) and its enormous sphere of influence (extending from Tijuana down much of Mexico’s Pacific coast) sets it apart from some of its more volatile competitors, and serves as a basis for its hegemony.

The answer to this question has serious implications for Mexico's security. Previous splits within the Sinaloa clique have spawned some of the bloodiest episodes in the country's recent history. The feud between Guzman and his former ally Arturo Beltran Leyva led to thousands of killings. Another split with former Guzman's former associate Vicente Carrillo, which stemmed in large part from Guzman’s murder of Vicente’s brother Rodolfo in 2004, helped turn Juarez into one of the deadliest cities on the planet.

Beyond the bloodshed, such internal quarrels, should they spread, have the potential to reshape the map of Mexico’s drug trade. If the Sinaloa splinter group were to secure the backing of an outside organization and wrest control of cities like Durango, Guzman and his partners could see an erosion of their power in Mexico’s underworld.