Sometimes an answer comes to the call. More often the supplies disappear overnight when more migrants are actively hiking out of sight of the Border Patrol. On one of the nights I spend here, 72 gallons are taken from a single drop point in one night.
The volunteers are with No More Deaths (No Mas Muertes), a loose organisation set up to provide humanitarian aid to migrants. The group emerged from the Sanctuary movement which assisted Central American refugees in the 1980s. They manage several situations, including an aid station on the other side of the border at Nogales which assists those being sent back into Mexico. "We formed out of a moral obligation to respond to the human rights crisis," says No More Deaths co-founder, the Rev Gene Lefebvre.
The camp near the tiny town of Arivaca, Arizona is strategically placed some 20 kilometres from the border (as the crow flies). The Tucson sector of the border is by far the most utilised. The vast majority of deaths have occurred in a 150 kilometre stretch between interstate 19 and the Tohono-O'odham Reservation. Last year alone, 380,000 migrants were apprehended here.
The Border Patrol worker I speak to estimates migrant numbers are higher, at 5000 a day. Of those, he says, "we catch about 3500. Most of them are bad people" he adds. Bad people? "Most of them are felons," he explains.
Early this year, Homeland Security made sure of this with the institution of Operation Streamline. New laws make crossing the border without papers a felony. The first offence usually sees the migrant returned to the south; a second conviction can mean between six months and 20 years in prison. Streamline hearings see 60-80 people convicted a day in Tucson's courts, usually in the space of two hours. Migrants are often shackled together. "This is a hateful period in our country's history," says Margot Cowan, a lawyer with the group.
The approach is intended to stem the tide of "illegals" by using prison time as a deterrent. So far it doesn't seem to be working. According to No More Deaths, 1086 bodies of migrants have been recovered in the southern Arizona desert since they began in 2004. More than 128 have been recovered so far this year. The body count only includes those found and noted by Border Patrol officers. The remoteness of the region means there are bodies out there that will never be found.
Arivaca camp is supported by friendly local ranchers and a steady trickle of volunteers from church groups and liberal colleges. Patrols are conducted daily, unless disrupted by sudden lightning storms, crippling heat, impassable roads, flash floods, or rattlesnakes. Hiking is dangerous here even with a GPS and plenty of water. Black Hawk helicopters circle overhead. According to one volunteer their use is a tactic of intimidation by Border Patrol which can separate panicking groups of migrants and cost lives.
The militarisation of the US-Mexico border has escalated in recent years, a shift that coincided with the signing of NAFTA in 1994. The "war on drugs" and the "war on terror" have furthered pressure on border control. The promises of free trade have been broken for many Mexicans. Economic pressure here in the US adds to anti-immigration sentiment. South-westerners complain of immigration as though it is a new phenomenon.
It is easy to forget that until recently, the border was porous.
Some 4-5 million Mexican nationals live in the US without papers. The vast majority are agricultural workers in California. Some estimates put their cost to the US economy in health care and social security at $15 billion a year. Others suggest their worth to the same economy is $1.7 trillion.
Enrique* has been living and working in Phoenix for 16 years. Six months ago, he returned to Mexico to take money to his family. A trip he used to make regularly has now become life-threatening. Forced to make the crossing illegally, he injures his knee in the desert. His left leg is swollen to twice its normal size. He knows he is slowing his group down, and could be left behind to die. He calls to a No More Deaths patrol for help.
Enrique cheerfully accepts rest on a camp cot, food, medical attention, and volunteers' attempts to negotiate with the Mexican Consulate. The Consulate can do nothing for him. They are having a busy week: a van has overturned on the highway carrying 15 people without papers. Nine of them have been killed. In the local newspaper, they are referred to as "illegals".
Humanity becomes relative in contested territory. In February, volunteers discovered the body of Josselina Janiletha Hernandez Quinteros, a 14-year-old girl from El Salvador who was separated from her group and who survived alone in the desert for two weeks before her death by probable suicide. "If she had been a 14-year-old girl from Tucson, that would have been front page news," laments LeFebvre. Now volunteers leave water beside a shrine erected to her memory.
The trek is becoming tougher every year as increased border patrols push migrants toward the mountainous region to the west. Meet points are retreating north, extending a 2-4 day hike to a 6-7 day one. It is physically impossible to carry enough water to survive.
Migrants are not only being pushed further, they are paying more. The cost has risen from $300 to between $1500 and $3000 for "coyotes" - leaders who know the trails. Enrique tells us the coyotes change their routes because they know where the water will be. "No More Deaths is famous in [the border town of] Nogales," he jokes.
Previously, No More Deaths would call Border Patrol to return sick or injured migrants south if they wished to give up their attempt to cross. Since Operation Streamline, that is no longer considered a safe option. Volunteers risk arrest for driving migrants themselves. The legal situation at camp is precarious: volunteers can give water but are not supposed to provide food; they can give directions but not maps. This week, volunteer Dan Millis is in court for leaving water in a national wildlife refuge. His charge? Littering, since changed to being in the park without a permit.
The US-Mexico border was drawn as result of several purchases in the mid-19th century which saw Mexico halved in size. There is now a wall being built along that arbitrary line. Since 2006, migrants are being fenced out. According to No More Deaths the wall has had a serious impact on the death toll.
"The primary reason the migrants, and No More Deaths, are out in these remote desert areas is because the policy of the United States has been to build large walls around the urban areas where people could easily cross the border. Now migrants are forced into the rugged desert mountains of southern Arizona - which has turned the region into a long graveyard," says their website.
As part of the wall strategy, Bush awarded a $20 million contract to Boeing Inc to build a "virtual" fence along the Arizona border. The 28-mile stretch was intended to use radars and surveillance cameras to try to catch people entering the country illegally. The system, called SBInet, has never worked. In response, the company has now been awarded a follow-up contract. They are referring to their failures as a trial period.
In Berlin last month, Presidential hopeful Barack Obama spoke in his usual impassioned style about that city's history. "The greatest danger of all is to allow new walls to divide us from one another," he said. "The walls between the countries with the most and those with the least cannot stand."
As a senator, Obama voted to support the legislation that enabled the wall in 2006. He changed his tune in the Texas debate in February, but spoke in favour of surveillance technology and patrolled borders. Demilitarisation does not appear to be on his agenda.
Come election time, it will be interesting to see whether Obama is willing to tear down a wall his own country is building between the haves and the have-nots. In the meantime, Mexico remains the scapegoat for the economic ills of the US. And of the thousands who continue to walk across that imaginary line every day, some will walk to their deaths.
*names have been changed
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