I arrive at the gas station in Three Points and spy a tall, unshaven, sweat-soaked Tim standing by the side of the road. My sense relief is huge and I hug him in spite of his wet, muddy clothes and his delightful smell of body odour. Here is his story of Tim’s second night and day in the desert:

We walked through the dawn, weaving through the mesquite and cactus wilderness, clothes soaked, shoulders burning, and down to a can of refried beans and four tins of tuna fish. We have no real sense of where we are.

We count a coyote and three deer bounding through the brush, but the only trace of human life are a tangle of muddy foot tracks left by migrants, perhaps several hours ahead of us on the trail, together with a litter of water jugs and tins in their wake.

By nine o’clock the sun is roasting, sucking the life out of us. We need to find shade, and settle on a patch of sand beneath a cat-claw tree. We strip off our wet clothes and hang them from a tree root, and carry out an inventory of our state.

My right hand has plumped up like a mitten, after something bit me during the night. Tomas’ feet have swollen in his new boots, and his shoulders “feel like pulp.” We set down the packs, lie down in the sand, close our eyes and we are out.

We wake around three in pain, swig down an anti-inflammatory pill a piece, struggle painfully into our dried-out gear, and force down some food: tuna, eaten off the knife, and our last tin of refried black beans, chunky like dog meat. We have more than 30 miles to go. As we struggle painfully back into our clothes, I wonder for the first time if we are going to make it.

Migrants who know they are beat try and find a road, flag down a truck for help. I look at Tomas wince as he puts on his shoes.

“Tomas, mate, I think we need to head toward a highway.” He nods knowingly… “

I spend the evening constantly ringing Tim on his cell phone, which is supposed to have infallible reception, but I get his voicemail every time. The thunder clouds gather again and the rain starts. For the first time I am genuinely worried about Tim. Only the sight of the full moon and its white light across the desert as the clouds clear gives me a weak hope that he can at least now see the way through the night.

Early the next morning I receive an email marked ‘URGENT’ from my Reuters colleagues in Mexico — Tomas’s feet have given out and he needs help. Tim has apparently rung through to a Reuters office somewhere and the message is to meet him at the Three Points gas station at midday.

Unable to get in touch with Tim via my sat phone, I can only assume he is all right and has chosen to sleep through the day and the heat of the desert to prepare for his second night’s walk. So I head back across the border back to El Sasabe to meet up with the Mexican government’s border wide migrant protection and rescue organization, Grupos Beta.

Orange-jacketed Beta agent Mario Moreno puts on a pair of sunglasses and fills his dented orange pick-up truck with water, first aid medicines, electrolyte solution powder packets and leaflets warning migrants not to attempt the walk through the desert. His job is to help those who have been turned back by the Border Patrol, give medical assistance and try to dissuade those who are thinking about crossing illegally into Arizona.

I can’t help noticing the truck’s missing headlights and rusty axles, a contrast to the Border Patrol’s shiny white vehicles that roam around the border on the U.S. side.

We head west along muddy dirt trucks, splash through puddles, charge up rutted slopes and slide through the sand. The desert is ostentatiously green and grass is even growing under the mesquite trees.

After an hour’s drive to what feels like the remotest place on earth, we turn through a chicken-wire fence and, surrounded by empty water bottles, tin cans, broken shoes, some hungry pigs and bits of rotting food, we come across dozens of undocumented migrants waiting for nightfall to cross.

There I meet Veronica Cruz, a Mexico City-resident preparing to walk the desert with her three-year-old daughter Evelyn. Little Evelyn lies asleep on a dirty wooden table in her pink socks and tiny denim jacket. They have run out of food and water after walking for eight hours to get to this farm, where migrants believe they have more chance of getting across unnoticed than from El Sasabe. I cannot help but think of my own two-year-old boy and how fragile young children are. Veronica has a cold from last night’s rains. She thinks it is only a four-hour-walk across the desert.

Even in the age of the Internet and all the information and maps it provides, it is amazingly easy to get lost, especially in the desert. So Tim tells me from his satellite phone, as I ask him how he got on during his first night walking across the border from my lodgings in the town of Arivaca in Arizona just a few miles from the border.

The news isn’t good.

“We don’t where we are,” Tim says anxiously. “I walked for about seven hours, going round and round, nearly stumbling into dangerously sharp cactuses. At first when I saw some footprints, I thought they were other migrants and I followed them. Them I realized they were my own. It’s like a cartoon.”

Last night, as he left El Sasabe, Tim hastily assured me that he knew his way through the huge expanses of undulated, rocky desert. He would walk along the main road through the Altar Valley, an unforgiving wilderness bounded to the east and west by rugged mountains that look a serried range of broken knuckles. Then he would cut into the Buenos Aires National Wildlife Refuge and follow a trail until he came to the road to Arivaca. From there, he would follow the river bed that runs parallel to the road until Three Points, a gasoline station in the desert where many people smugglers pick up illegal immigrants and shift them to Tucson and Phoenix.

It all sounded so simple. So simple, in fact, that Tim forgot to take out his compass.

“I thought I was heading out into the desert and expected a fire pit. I expected to see coyotes and wild deer and to walk under the light of the full moon. But as I walked through the thunderstorm in the pitch darkness, I heard nothing but a cacophony of toads. I probably crossed five or six normally dry river beds that were ripped open and flooded by the rain,” Tim says.

With his shoulders aching from the heavy backpack and his skin beginning to itch from being soaked through, Tim tells me he has found his compass and will find the Arivaca road. But his morale gets another blow. “Damn! I forgot the tortillas,” he says. “Who knows how I am going to eat my tuna and frijoles rations now.”

We leave Altar for the remote border town of El Sasabe, where the migrant hopefuls start their walk into the United States. “You are going into the lion’s den”, says a coyote with five years in the trade, whom we meet eating his meat tacos at a roadside restaurant and who talks about those who have died trying to cross the desert.

That doesn’t seem to put anyone off. At midday in Altar, the rusting brown and white Ford vans that shift up to 1,500 migrants a day up to the border cough into life. They pack in the people. With bare metal benches running up each side of the vans and a bench up the middle, about 20 grown men crouch inside each vehicle for the hot, bumpy, three-hour ride to the border. Cost of a ticket: 100 pesos ($9.00) each.

Tim tries to talk his way into letting a driver take him with the migrants. Raising suspicions that the tall white gringo might be from the migra or just completely mad, he is rejected, so Tim takes his pick up truck and Tomas and I drive the hire car. We turn off the paved highway. A rusted sign saying “Sasabe” points us down a wide dirt road through the desert.

At a concrete hut, we pay 30 pesos ($2.50) to a old man in white cowboy hat. He lifts up the chain.

We feel shaken to bits by the furrowed road. Our wheels skid in the sand. The dust blinds our windshield. Dozens of vans hurry past us, their worn tires bouncing in and out of pot holes as they barrel down illegal immigration’s superhighway.

Until they arrive at the lake in the middle of the road, that is. One by one, the vans rock through a chocolate brown mess of mud, tire tracks and water from the heavy rains the night before. Tim’s truck makes it through easily.I, in the pathetically unsuitable hire vehicle, try.I rev through the sticky soup, hold the steering wheel steady.I get stuck, my wheels spin and the chassis sinks into the mud.

Two men wander over with a chain and offer to haul us out, but there is nowhere to attach the chain, so I try to reverse, get some traction and have another try. I make it out.

Tim gets a puncture. We fix it in the searing heat and it is some comfort to see a handleful of vans along the route with tire problems too.

We pass rusted wrecks of abandoned cars in the desert, rubbish, empty water bottles, dead animals and migrants with candles to Mexico’s most hallowed saint, the Virgin of Guadelupe. We rumble into El Sasabe.

Along the dirt, rutted back streets of Altar, the heat is incessant. The cartons of fruit juice in our bags are warm as hot water bottles. There is no shade for the dozen or so Central American migrants lining up outside the Catholic Church-run migrant shelter in search of a meal and bed to crash in.

Their shadows fall on a monument outside the shelter’s concrete façade to those who died crossing the desert. “In memory of those who, by seeking a better life found only death” reads a rusted plate of metal.

We go inside and meet the migrants, many with weary faces, exhausted after 20 days of riding freight trains up through Central America to get to the Altar, hanging on the wagons day and night and knowing that falling asleep could mean falling off the trains and, well, probably death.

Shelter manager Marco Antonio invites us to a simple dinner of tuna, vegetables and rice and of course tortillas and plenty of chili, cooked by church volunteers. Around a long plastic white table in a big, bare hall, we say grace and, with everyone’s baseball cap taken off, tuck into the food.

Between fork fulls of stew, Jokeli Antonio Cunza, a 20-year-old farm laborer from El Salvador explains why he wants to start a new life in the United States. It is not just because of the poverty, the earthquakes, the hurricanes, the corrupt politicians and the droughts, he says. It is has a lot to do with boredom.

In his remote village near the Izalco volcano in El Salvador, Jokeli, who has a bright smile and a smattering of English, gets up every day at 6:30 a.m., eats his breakfast of bread and coffee, and goes off to work on his grandfather’s farm. It is boring work. He pokes holes in the ground with a stick to sow corn seeds, he picks mangos, he weeds the ground. Then at 4 p.m. he goes home, has a lunch of rice, beans, and once in a while chicken, and watches soap opera reruns on television until 10 p.m. Sometimes a few friends will kick a football around.

“There is nothing to do, no jobs, no future, no nothing. The boredom is crushing. We all want to leave,” says Jokeli, who dreams of speaking fluent English, starting a small business and climbing the Empire State Building in New York.

REUTERS photos by Tomas Bravo

Along with water, willpower and a strong pair of legs, a backpack is what almost every undocumented immigrant carries through the Sonora Desert.

Miles from the nearest store or restaurant, unable to cook on a camping stove for fear of attracting attention and under the searing heat of the sun in the day, migrants take a mix of lightweight nibbles, medicines, sweets and electrolyte solution to help them make the trip.

At the main supermarket in Altar, an impressive, well-stocked store for such a humble place, we spoke to poor Mexicans preparing to walk the desert who were buying food for their trip. Here is what is most of them put in their backpack, which can be bought for $5 at any of a dozen stores that line the shabby town`s streets.

A couple of tins of tuna

A packet of electrolyte powders, a vital combination of sugar and salt to avoid or recover from dehydration

A kilo of raw brown sugar

Packets of beef jerky

Garlic

Gatorade

Chocolate bars

A packet of tortillas

Two gallons of water

Undocumented migrants rub the raw garlic on their trousers to keep snakes, scorpions and coyotes away.  Some take energy drinks such as Red Bull, although taking the drink is counterproductive, the Red Cross in Altar says, as it means people dehydrate more rapidly. The days of carrying wads of cash in backpacks to help an illegal immigrant is his or her new life are over, as bandits cruise the desert and seek to rob the migrants.

Like would-be migrants from across Mexico, we spent $15 each on supplies of food and water for the three-day trek. We also shopped around and bought long-sleeved shirts, cotton neckscarves and baseball caps for shelter from the sun, and a $5 rug to sleep on the desert floor. Total cost, $16.

REUTERS photos by Tomas Bravo

Stuck out on the main highway at Altar is a free clinic run by the Mexican Red Cross set up in tractor trailer. Tomas, Robin and Tim seek out volunteer paramedic Amado Marcelo who treats migrants sent back by the Border Patrol, and offers checkups for those heading up on the three-to-four-day desert walk.

Of the thousands of people who trek through each week, the salt and pepper haired medic from Hermosillo sees people of all ages. Men and women, some heavily pregnant or with young children, and even people of retirement age, all head up to the border.

“The first thing I tell them is, don’t go.” The desert is very dangerous, and we don’t want them to get stuck there, but they are very determined,” he tells me as he prepares to check my blood pressure, pulse and heart before we head up to the line tomorrow.

If he can’t dissuade them from going, Amado gives them advice for the best possible care on a trip where temperatures reach 120F. He tells migrants to take small, regular sips of water and gives them rehydration salts. He has a tip for us on how to avoid blisters.

“Take several pairs of socks and change them every time your feet get damp,” he tells Tomas and me, signing us both off with a more or less clean bill of health. I have slightly high blood pressure, and Tomas is already sweating and a bit dehydrated by the heat.

REUTERS photos by Tomas Bravo

It is one of the truly emblematic journeys of our times, although it never makes it into the travel pages of any newspaper: the million or more people who make the trip each year are poor Latin Americans, trekking north from Mexico, albeit illegally, in search of a better life in the United States.

The trail begins in cities, towns and villages throughout the region where many residents get by on a few dollars a day, and winds its way north to staging areas just short of the 2,000-mile (3,200-km) U.S. border.

Join U.S. immigration correspondent Tim Gaynor, U.S-Mexico border correspondent Robin Emmott and photographer Tomas Bravo as they follow in their footsteps, crashing in flop-house hotels and heading on out across the Sonora Desert on foot.

Their journey starts in Altar, the dusty and chaotic clearing house in Mexicos northern Sonora state, through which tens of thousands of migrants pass each month en route for the porous U.S. border, many with little more than a day sack full of tortillas and a gallon jug of water.