They call it the "corridor of death". At one end is poverty. At the other the American dream. And in between there are drug gangs, killer temperatures for a three-day walk across the desert and hostile border guards.
But each day, hundreds of people arrive in Sasabe from across Mexico and Central America, hoping to reach the US and in many cases ready to carry a backsack full of marijuana with them.
Clandestine immigration and drug trafficking play major economic roles in the towns of Sasabe and Altar in Sonore state, on the Mexico-US border.
The US non-governmental group, Humane Borders, estimates that the Sasabe valley is the main point for illegal entry along the 3,000km US-Mexico border, because the Arizona desert is the least patrolled border sector.
But crossing the border involves a three day walk, with summer temperatures soaring past 50oC and the trekkers risk dehydration. Border patrols are also waiting.
Shops in Sasabe sell creams for muscle pains, special jackets, flashlights for nighttime walking, and black paint to mask out anything that might shine and give away the wouldbe illegal migrants.
Across the border, the waves of illegal immigrants have sparked a fierce political debate that has divided US President George W. Bush's ruling Republican Party.
There are an estimated 11.5 million undocumented workers in the US and hundreds of thousands have taken part in demonstrations against a bill that has passed through the House of Representatives and would make illegal entry a crime.
The Mexican authorities are also unable to cope with the march to the frontier.
"You need the federal police here. They are too few for the number of migrants and the amount of drugs," said a member of Beta, a group created by the Mexican government to aid migrants.
Altar, 100km west of Sasabe, is dubbed the "ante room" of illegal immigration, explained Prisciliano Peraza, a priest, who calculated that there was a "floating population" of about 7,000 wouldbe migrants.
Sasabe, with some 3,000 permanent residents, resembles a shanty town lost in the middle of the desert. The migrants often take shelter in wooden shacks and tents while they wait their chance.
Drug gangs lurk seeking to recruit human "mules" to carry consignments across the border.
"Groups of 15 `mules' from the Sasabe zone cross the frontier, each with 20kg of marijuana on their backs," said Jose Antonio Rivera of the Commission to Aid Migrants in Sonora.
"Young people are recruited here, in the cities and villages of Sonora. They deposit the cargo in the US, then they hand themselves in to the US Border Patrol, which takes them back to Mexico." Rivera said.
"They earn US$1,000-US$1,500 for each trip," he said.
Mexican authorities say that they are overwhelmed by the smugglers.
According to aid groups, more than 3,000 people cross the border each day.
The "coyotes," who guide the mules across the border, rob newly-arrived recruits, many of whom are illiterate and terrified peasants.
"They are afraid because the `coyotes' say that if you speak to someone, the police could stop you even if you are Mexican," said Julio Castro, an inhabitant of Altar.
"Then they rob them at gunpoint and steal their money," Rivera said.
But for the mules and immigrants alike the lure of money or a better life in the US is enough to spur them across the desert.