"We're living desperate times here. They're not letting supplies through.... We're down to basics, beans and potatoes," said one longtime female resident of Tubutama, a pueblo perched on a mesa and known for its white-washed mission church and plaza, where locals and visiting Americans on mission tours once sipped drinks and listened to bands on summer nights.
The two cartels are warring over Mexico's most valuable region for smuggling people into the United States, with an infrastructure of drivers, guides, suppliers and fleabag hotels that has pumped millions of immigrants across the border. Each cartel has allied itself with local gangs with names like the Wild Boars and the Masked Ones.
In the scorching valley south of the foothills, most residents appear to have sided with the Sinaloa group, saying they at least have brought order to the messy business of smuggling drugs and people across the border.
Cartel toll takers monitor the Altar-Sasabe highway leading toward the frontier, making sure each immigrant-loaded van has paid the $100 fee for each. Rogue gangs that preyed on vulnerable immigrants have been chased out by the cartel, say some residents and immigrant safety groups.
Life in the valley follows a relatively secure, if hyper-vigilant, routine. When a pair of reporters walked through the town of Pitiquito a day before the convoy hit the road, a pack of teenagers and men wielding a club and a baseball bat descended on them.
"Whose side are you on? What are you doing here?" one of them asked.
A middle-aged woman walking with her teenage daughter later explained that the town was controlled by a young Sinaloan crime boss greatly respected by residents. Two of his gunmen had joined hundreds that afternoon in a funeral procession for a popular musician killed in an accident. The crime boss probably paid for the funeral, she said.
"He's the one on our side" of the war, one woman said. "He is a generous man and protects us. Nobody is even allowed to sell drugs here. Everybody loves him here."
In the sparsely populated foothill towns known as the pueblos de arriba, the towns up above, expressing such sentiments can be lethal.
The government force began its steady ascent on the two-lane road and passed through the pueblo of Atil, where many residents avoid using telephones, believing the cartels can listen in.
One former resident, a middle-aged woman, said her son was kidnapped and killed this year, and that the family had to flee with a mattress strapped to their pickup truck. Though she's concerned for family members left behind in Atil, she won't call them.
Her son, she said, was slain execution-style and left on the side of the road.
"We haven't taken sides. We're not with one group or the other," said the woman, who asked that her identity and new home not be disclosed. "That's why I don't understand what happened. There are no answers."
The convoy passed Atil without incident, but as the road ascended further, the landscape began revealing signs of neglect and cartel activity. Vegetation and rocks from landslides encroached on the roadway; signs were defaced and gasoline stations abandoned.
Outside the community of Cerro Prieto, the roadway cut through a hilly area where the war's grisliest massacre occurred.
In July, Beltran-Leyva gunmen took positions above the road where 20-foot embankments provided an ideal ambush overlook; a convoy of Sinaloa gunmen approached. As the cars passed, the gang blockaded both ends of the road and opened fire on their boxed-in enemies. Twenty-one Sinaloa cartel members were killed. Based on the thousands of spent bullet casings, police estimate that there were more than 100 attackers.
New patches of black asphalt cover the blood. The convoy's drivers speeded through the embankments, careful not to bunch up their vehicles and leave them vulnerable to a similar ambush.
Attempts to root out the criminals have been frustrated by the rough terrain and guerrilla-style tactics used by the shadowy force, say federal and state agents. The gunmen strike and then rush back into the gullies and hills dotted with towering saguaro cactuses and mesquite patches.
"When we go up after them, there's nobody there. We can't find them," the high-level Sonora law enforcement official said.
The gangs seem to know everything. The federal police, who wear blue uniforms, overhear the chatter of cartel lookouts on their radios, reporting their positions with unsettling exactitude.
"They say, the blues … are heading your way," one federal police officer said.
"We know they're watching us, but we can't see them."
Turning onto a dirt road, the convoy approached the village of Saric, the deepest point in cartel-held territory.