They move at night, when it's cooler and the moon's glow can guide them from Mexico onto an Indian nation so vast that many easily slip through a flimsy barbed wire fence unnoticed.
''It's like the desert doesn't sleep,'' tribal police officer Darrell Ramon says, peering into the night as he drives through the nation's isolated communities. ''It wakes up at night. Bodies start moving out there. You see headlights way in the desert.''
Despite a strong Border Patrol presence, the immigrants still come.
It's easier here, they say. Here, they find tribal police officers who are overwhelmed. Money is scarce for this tribe, and there is little help from the federal government.
The Tohono O'odham people are tired, exhausted with truckloads of immigrants trashing their land, raiding their homes and stealing their cars. The flow never stops. Not in a place that shares 75 vulnerable miles of the U.S.-Mexican border.
Deep in desert: Deep into the Sonoran, Ramon drives over hilly dirt roads riddled with potholes, never sure of what he will find. Often, it's a group of exhausted immigrants waiting for their ride to freedom. Or lost, disoriented men who find their way to the main roads, begging for help. Occasionally, a family out of food and water. Then there are the bodies. Last year, 51 people succumbed to the pounding Arizona heat.
''It's an everyday thing out here. It's constant from sundown to sunup,'' he said.
Indian County makes up only 2 percent of the country, but tribal lands encompass more than 260 miles of international borders. Thirty-six tribes have lands that are close to or cross over international boundaries with Mexico or Canada.
Tens of thousands of illegal immigrants cross these borders and disappear into the heart of Indian Country each year, according to the National Congress of American Indians.
And tribes feel they are on their own, left with easy routes into America and not enough money to do a job the government should be doing.
This reservation is part of the Border Patrol's Tucson sector - the busiest place in the country for illegal border crossings. Last year, more than 491,000 illegal immigrants were arrested in this area. Combined with arrests in Yuma to the west, the numbers make up more than half of all immigrants arrested in the entire country.
But many - Indians say most - are never caught.
''They know they'll most likely get through,'' Ramon said.
When you reach the border, not far from the main reservation town of Sells, a barbed wire fence extends as far as the eye can see in either direction. A Border Patrol agent sits in his SUV under a tree, waiting. A helicopter buzzes overhead, dipping low into the desert.
An old pickup truck rumbles up toward the Mexican side. Tribal member Harriet Toro hears the rattle before anyone else.
''Listen,'' she says, looking into the emptiness.
The truck approaches, perhaps just for a look, then turns back.
Much poverty: There are 24,000 Tohono O'odham members, and 14,000 live here on the reservation. Forty percent live in poverty and many members still lack basics such as running water and electricity. Obesity and diabetes are rampant. Unemployment is 42 percent, and only 52 percent of students graduate from high school.
An hour southwest of Tucson, it's another quiet evening in Sells. The summer heat is relenting and women who sold their homemade tacos in the vacant lots are packing up for the day. The community gym is filling with after-work fitness buffs and children walk along the streets. Commuters are making their way home, often to some of the 60 villages that make up this reservation of 2.8 million acres - the equivalent of the size of Connecticut.
Each year the tribe spends more than $3 million dealing with illegal immigrant activity, from finding immigrants, offering medical help and paying for autopsies to hauling away trash and abandoned vehicles. Immigrants take up 60 percent of the tribe's law enforcement time.
The tribe would rather spend all that money and time on health care, education and housing.
From 2001 to 2004, the tribe received $310,613 for homeland security planning, training and equipment purchases. This year, the Interior Department gave the tribe $1.3 million to help control immigration.
But that was not even half what the tribe will spend for the year.
''We're bending over backwards to help the United States, to protect the public and we're not getting any help,'' said tribal Chairwoman Vivian Juan-Saunders. ''If this happened in any other area of the country, it would be viewed as a crisis. But it's the fact that it's in Indian Country.''
Arizona's governor and Sen. John McCain, R-Ariz., have also complained about the lack of funding, with McCain calling it ''disgraceful.''
Yet McCain also said the money has to be given where the greatest risk is, ''and the greatest risk is not a lot of Indian reservations.''
Trouble begins: The trouble began for the Tohono O'odham people when the government started cracking down on illegal immigration into California and Texas in 1993.
With more agents and helicopters on duty, smugglers had to find other routes. They were forced onto remote federal and tribal lands, where they know there are fewer resources and more chances to slip across the border.
''These individuals are going to use the covers of darkness, the shadows of the deep canyon,'' said Mario Villarreal, spokesman for the U.S. Customs and Border Protection. ''That's why they move to these isolated portions of the border.''
The result is a land overrun with immigrants. The Tohono O'odham estimate 1,500 people each day cross the border into their reservation. Last year, more than 400,000 pounds of marijuana were seized and 141 immigrants died in the Tucson sector, according to the Border Patrol.
More than 2,300 Border Patrol agents are assigned to the Tucson area, up about 800 agents from 2000. By the end of the year, 534 agents will be added to the Arizona border.
The tribe and the Border Patrol often have a love-hate relationship. Tribal members want the Border Patrol to do its job, but tire of the constant helicopters and getting stopped on their way back and forth across the border, where the Tohono O'odham's land extends. They also say the Border Patrol shouldn't have access to the tribe's sacred sites.
But the head of the Border Patrol's union said the tribe is a difficult partner and could help itself more.
''They need to make a decision whether they want to be part of the team or treat themselves as a foreign nation,'' said T.J. Bonner, president of the National Border Patrol Council.
He opposes giving the tribe the direct homeland security funding it wants, saying it doesn't have the expertise to deal with illegal immigration.
The Border Patrol insists it works well with the tribe, but a Government Accountability Office report on border security last June found that federal lands agencies, Border Patrol and tribal governments lack coordination and that land management agencies believe funding to prevent illegal crossings has been insufficient.
Scary scenes: When the desert turns to black and Royetta Thomas rounds the corner to her street in the tiny community of Miguel, she shudders at what she might find. Her house backs up to the Sonoran, and immigrants often use her spigot to get water. Twice, her house was broken into, her window busted and food, shoes and jewelry stolen.
This is the burden of living in the path of the busiest border crossing area in the country.
''Now it's like you don't even know who's watching you,'' she said from her front yard. ''I'm just wondering what's next? We have no privacy.''
Everyone here has similar stories: The time immigrants were found hiding in a large trash bin, waiting for their ride, or when immigrants stole clothes from a clothes line so they could look American. One brave soul swiped food off the stove as it cooked.
Many say they struggle with how much to help desperate immigrants, and the tribe even battles its own members who can't resist easy money for hauling a load of immigrants or drugs. Last year, more than 130 tribal members were arrested for smuggling.
Tribal patrol officer Mario Saraficio is a few hours into his shift when he gets a call. A blue Chevy truck loaded with immigrants has been spotted on an isolated stretch of dirt road.
He flies through the desert, past the empty water bottles, shoes and clothes strewn about. There are fewer piles of trash since the tribe received a federal grant two years ago to clean them up.
Still, the tribe estimates trash sometimes amounts to 6 tons a day. Abandoned cars, some burned and overturned, haunt the reservation. Last year, more than 1,700 cars were left here. Some sit for months, waiting for the tow truck.
''To us, the earth is very sacred,'' said Verlon Jose, a tribal council member. ''It's not only damaging physically, but spiritually and emotionally when we see these things.''
The blue Chevy proves elusive. No telltale dust on the roads, no movement in the still desert.
A strange lull has settled on the reservation in the past few weeks. Unusual, Saraficio said. But it won't be for long. They've probably just moved to another spot.
Then, almost out of nowhere, an immigrant emerges up ahead along the edge of state Highway 86. He is Jose Gonzalez, a 44-year-old father of five from Acambay, Mexico. He wears new hiking shoes, a worn backpack and a grin. For four days, he walked off and on to reach America along with 11 other people. They got separated, and Gonzalez was robbed of almost all the $1,200 he was to pay the smuggler.
He planned to make his way to Chicago and work as a landscaper. Now he is thirsty, hungry and giving up. The Border Patrol whisks him away to be sent back home.
But, he says, he will try again next week.
The officer eases back into his SUV and heads back out into the night, knowing there will always be another just like Jose Gonzalez.
For the Tohono O'odham, it has become a way of life.