They stream in. Today, the same as yesterday. The same as the day before. Backpacks are stuffed with bottled water, soap, chips, maybe an icon of the Virgin of Guadalupe. They wear sweaters and wool hats for the cold desert nights.
It often starts here, in Altar, 60 miles south of the Arizona border, at one of the largest staging points for would-be migrants attempting to cross into the US illegally. The travelers arrive from all over Mexico, Central America, even as far away as Colombia, and Brazil.
They are going to "El Norte." They tell you that, straight out. And if they don't cross this time, they will simply try again.
While debate in the US continues over immigration reform policy, here, on the south side of the border, there seems to be consensus that enforcement measures will deter almost no one. "Walls and lights and sensors and police fill our heads," says Dagoberto Martinez, "...but they don't make us turn back."
As President Bush heads to Mexico to meet with his counterpart Vicente Fox this week, the US Senate has begun a full-blown debate on immigration and border security. The suggestions range from creating a path to earned citizenship and a guest worker visa program on the one hand, and embracing tough enforcement measures such as erecting fences along the border, and treating illegal immigrants as aggravated felons, on the other.
The border patrol caught 1.2 million would-be illegal immigrants in 2005; that's an average of one arrest every 30 seconds. There are no official stats for how many made it across, but the Pew Hispanic Center estimates there are, today, between 11.5 and 12 million illegal immigrants living in the US, of whom 56 percent are Mexicans.
From Altar, some, going it alone, flag down buses headed north, where they will try to sneak across. Others - the majority, according to the US Border Patrol - have hired coyotes, or people smugglers, to guide them. These travelers get on vans and are shuttled to whatever point along the border has been chosen for them that day.
Maybe they will walk across near Naco, Mexico, and into the canyons beyond, or perhaps they will trek through the rugged mountains around Organ Pipe Cactus National Monument toward Highway 8. They might take the increasingly popular Sasabe route, following "ghost roads" in the sand toward Tucson, or even try the Barry M. Goldwater Air Force Range, a live bombing ground, and head to Yuma, Ariz.
Often, these travelers don't even know where they are along the route, many admit. All that matters is the final destination.
The first time Jesús Ramirez sneaked into the US was three years ago, when he was 17. He found work in Las Vegas doing construction work during the day, making $200 a week, and busing tables at night, adding another $150. Back home, in Michoacan, Mexico, says Ramirez, he never made more than $80 a week. He now sends half his money back to his parents every month, and saves most of the rest for trips home at Christmas, and to pay the coyotes to help him back across when the holidays are over.
Last week, together with a dozen others, Ramirez set off from Michoacan. He will pay the coyote $1000 upon arrival in Vegas, he explains. From Altar his group drove to near Sasabe, and across they went.
The temperatures plummeted, Ramirez says. They walked single file. No one spoke. Finally, after three long days of this, they were apprehended by an agent in a big sports-utility vehicle. Ramirez was almost relieved, he admits. The coyote managed to escape. The rest were driven to Nogales, Ariz., processed in four hours, and without ceremony, shown the gate back into Mexico.
Now Ramirez is at the Mexican immigration police headquarters in the town of Nogales, Mexico and starting to think about a ride back to Altar. Next week, he says, he will try the whole thing over again, but on a different route. He has a T-mobile cell phone number. Call it in a week or two, he suggests, and he will be back in range, on the other side.
There has been a great deal of change in the Yuma sector since agent Mike Gramley came here 12 years ago with the border patrol. Back then, there were 300 agents who would follow footsteps in the dirt track roads, and a newly erected fence that ran for six miles around the urban areas - resulting in 50 apprehensions a day.
The pace of change has been furious in the last year: the number of agents in Yuma has more than doubled to 650, and the existing fence is being elevated to 12 feet and extended to 10 miles. An all-purpose road is being paved, a secondary fence is going up, stadium lights shine spotlights throughout the night, motion sensors are buried in the ground, surveillance planes fly overhead, and high-resolution infrared cameras beam the slightest movement back to control rooms at headquarters.
Meanwhile, 6-1/2 feet tall vehicle barriers - made of galvanized steel and filled with a special resin that prevents them from being cut - are driven seven feet into the ground and four feet apart all the way to Cabeza Prieta, 125 miles along the border.
Apprehensions have soared. From October 1, 2004 through September 30, 2005, 138,460 individuals were caught illegally crossing the border in the Yuma sector.
But to what extent does this mean fewer illegal immigrants are actually getting across?
Proponents of a fence argue that these preventative measures can be effective, and point to the San Diego sector as proof. There, after the creation of a fence and a beefing up of enforcement around the point of entry in the early 1990s - part of Operation Gatekeeper - that sector saw the number of attempted crossings plummet. In 2005 126,910 illegal immigrants were apprehended in this sector, according to the border patrol, compared with a peak of 629,650 in 1986.
The problem with this, though, say critics, is that such measures only serve to push the human traffic elsewhere. Operation Gatekeeper did drastically cut down the number of illegal immigrants trying to cross near San Diego, but this only sent people to Texas. Beefed up patrols along the Texas border soon pushed the traffic away from El Paso and toward Nogales and Yuma. Today, close to half of all illegal crossings take place in Arizona.
But, with increased vigilance near entry points and urban areas in this state, illegal immigrants try crossing in more difficult terrain - in locations where temperatures during the summer months often rise into the hundreds and never drop.
A record 473 migrants died in 2005 while crossing the US-Mexico border, the most since the Border Patrol began tracking such deaths in 1999. Heat exhaustion accounted for 168 of the 473 migrant deaths, and 12 died of exposure to the cold. Oftentimes, victim's bodies go unidentified and relatives never know what happened to them.
"Our mission is to secure the border - it is certainly not our goal to push the migrants to cross in more dangerous areas," says Gramley. "But it is also clear that that is what is happening."
Also, by making the journey more difficult, the coyotes become more necessary, and can charge higher prices. This, in turn, affects how long migrants stay in the US as they work to pay back crossing fees. According to Mexico's National Population Council, illegal immigrants stayed in the US an average of about six months during 1993-97. Those stays had increased to more than a year by 2001-04.
Back in Altar, Dagoberto Martinez is standing on the side of the road looking south, toward home. He is 17 years old, and like the Ortiz brothers, from Hidalgo. It's his first time here, his first time away from his brothers, his first attempt at crossing a border. He is not scared, he says. But he looks scared.
He will go to Los Angeles. There is work there and a second cousin too. At home, he says simply, there was no work. He shifts his gaze. "That's my whole story," he says.
• Ms. Harman is Latin America correspondent for the Monitor and USA Today.