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.