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