Northern Sonora state is just north of what is known as Mexico's "Golden Triangle," a region of the Sierra Madre Occidental Mountains responsible for high levels of drug production, particularly marijuana. The majority of drug shipments reportedly arrive in Puerto Penasco. From there, shipments are either taken east to border crossings in Agua Prieta, Sonoyta, San Luis Rio Colorado and Nogales, or they are simply shipped by foot north through the desert, where there is comparatively less law enforcement.

The Sinaloa Federation gained control of northern Sonora state after supplanting the now-defunct Beltran Leyva Organization in 2010. But the sparsely populated region requires only a few Sinaloa Federation members to oversee operations. Sinaloa lieutenants manage local, independent criminal organizations for trafficking marijuana, while more lucrative drugs go to points of entry such as Ciudad Juarez and Tijuana, with more Sinaloa oversight. Sinaloa lieutenants ensure that local criminal groups buy Sinaloa products exclusively, but these groups are not particularly loyal to Sinaloa; they would not object to buying drugs from Sinaloa's rivals. Moreover, local criminal organizations commonly fight one another for territory — independent of the larger cartels' machinations. 

While the motives behind the violence in northern Sonora remain unclear, similar events in the past have suggested the involvement of rival cartels. For example, on July 19 the brother of Raul "El Negro" Sabori Cisneros, a Sinaloa Federation lieutenant arrested in April 2011 in Hermosillo, Sonora state, was killed in a shootout. Several gunmen and an armored vehicle were used in the attack against the Sinaloa operative, indicating the possibility of a rival incursion. Those that would try to encroach on Sinaloa territory include Los Zetas; the Vicente Carrillo Fuentes organization, aka the Juarez cartel; and splinter groups of the Beltran Leyva Organization, such as the Cartel Pacifico Sur, led by Hector Beltran Leyva, or Los Mazatlecos, led by Fausto Isidro "El Chapo Isidro" Meza Flores. These groups operate in southern Sonora state and northern Sinaloa state.

While a turf war would necessarily lead to more violence in northern Sonora state, the violence would not be as severe as it is in more urban, populous areas such as Nuevo Laredo, Tamaulipas state; Ciudad Juarez, Chihuahua state; and Tijuana, Baja California state. Still, Sonora is a crucial corridor for trafficking illicit drugs and an important buffer for the much more valuable city of Tijuana, which is likewise under Sinaloa control. Sinaloa would carry out reprisals in the state for any encroachment on its turf. Therefore, if the violence in northern Sonora is the beginning of a larger offensive, the events of the past week could be a precursor to much more violence in the region. 

Editor's Note: This analysis was updated Oct. 2 to account for the Arizona shooting.