BBC NEWS
Fortress America's problem at the border
By Matt Frei
BBC Washington correspondent
Illegal immigration has become a major problem in much of the developed world. The US believes a million and a half immigrants cross its borders illegally every year. The majority of them do not come through its tightly-controlled airports - they wander in across the long and porous border which separates the US from its southern neighbour, Mexico.
It is always the unexpected detail that one remembers.
The bottles of Hellman's mayonnaise, strewn between the Saguaro cacti like the remnants of some hastily abandoned picnic.
"What's with the mayonnaise?" I asked Garrett Neubauer, the ex-marine turned border patrol "agent", as he insisted on being called.
He was spitting mouthfuls of phlegm pickled with chewing tobacco onto the parched ground when he was not trying to explain his mission to protect America from illegal aliens.
"They just love mayonnaise, these people. Mayonnaise and Taco chips. They also like this." He pointed to an abandoned sachet of caffeine pills.
"The coyotes, the people smugglers, give 'em these to speed them up. Trouble is, it kills 'em. Dehydrates 'em real fast!"
We were standing on top of a hill in the Arizona desert under a vast blue sky.
All around us Saguaro cacti, the ones that grow arms and look as if they had been painted by children, were standing sentry.
In the distance you could see a huge white building.
The locals call it the Taj Mahal.
It is the border post between the US and Mexico. It graces a pristine, asphalted road, the legal route between the two countries.
It was completed after 9/11 and hardly anyone ever uses it. The customs officials sit around playing cards.
Cat and mouse
But on either side of this monument to futility, the flimsy barbed wire that separates the First World and the Third has been prised open.
The churned-up sand shows a veritable stampede of migrants.
In the high season, which starts after Epiphany, as many as 6,000 Mexicans and other Hispanics will sneak across the border.
It is a game of cat and mouse, in which the mouse tends to win
Only one in three gets caught. It is a game of cat and mouse, in which the mouse tends to win.
We were spending the day with the border patrol to see how they catch the "illegals", as Agent Neubauer called them.
But we were having little luck.
Our brand new Humvee patrol vehicle got a flat tyre and the helicopter was "10-7".
"10-7? What does that mean?" I asked the agent, whose eyes were hidden behind wraparound reflector specs. "It means it's broken down, Sir."
No migrants, then.
But we did find plenty of traces.
You wonder how desperate or tired some people are to ditch the few precious
personal things that they have taken on this trek
Garrett Neubauer
The hill we were standing on was a staging post after the first two days of walking. From here, it is another three days to reach Phoenix, the capital of Arizona.
It looked like a municipal rubbish dump, strewn with precious personal belongings.
Rucksacks containing documents, family photographs, medication. A pink Slumber Party children's bike with a flat tyre.
Agent Neubauer shook his head. "You wonder how desperate or tired some people are to ditch the few precious personal things that they have taken on this trek."
The biggest disincentive to cross what has been called the "Tortilla Curtain" is not the border patrol, but the desert itself.
Every year about 600 migrants die, mainly from thirst. In the summer, the temperatures in Arizona often soar to 40-45C (104-113F).
The most astonishing aspect of this migration is the scale of it.
Last year, one-and-a-half million illegals entered the US.
At America's airports, they take your fingerprints and do a retina scan. They require new visas that involve longer queues.
The number of foreign students studying in the US has shrunk by a quarter since 2001. So walking across the border in the middle of the night is still the best option.
It makes a mockery of the concept of Fortress America.
But the US needs these people. And they need the US.
Vital work
To see why, all I had to do was look down my street from my house in Washington this morning.
Next door, there were five Latin American men grappling with long ladders. They had come to clear our neighbour's gutters, still clogged with autumn leaves.
They were wearing blue jackets emblazoned with the company logo, The Gutter Gang - and were trying to understand what their employer was saying in broken Spanish.
On the other side of the road, two Mexicans - or were they from Honduras, Nicaragua, Guatemala or El Salvador, it is hard to tell - were using a machine to blow leaves into a large heap.
Antonio the tree man was due to turn up at our house at ten o'clock, to cut some dead branches.
He is from Colombia. His partner Jose comes from Chile. Our plumber Francisco is from Bolivia. His wife Rosa works at a McDonalds in Maryland.
There is a film out this year called A Day Without Mexicans.
Based in California, it imagines how the Golden State wakes up one day to find that all of its Mexican migrants have disappeared.
There is no one left to flip the burgers, clean the loos, blow the leaves or nanny the children.
For 24 hours, life in California grinds to a halt.
Mass hysteria breaks out.