These volunteers search for migrants who go missing trying to reach the U.S.
JUDY WOODRUFF: Perhaps the biggest campaign promise President Trump has called for action on is building a wall along the U.S.-Mexico border.
Jean Guerrero of KPBS and the Fronteras desk — it's a public media partnership — discovers crossing the border is already a dangerous journey, as she joins a group of immigrants patrolling vast swathes of desert from California to Arizona.
JEAN GUERRERO: Marco Antonio Garcia vanished while crossing the border weeks ago. Maximo Garcia shows me a text message from a drug mule with a crucial clue about his missing grand-nephew.
MAXIMO GARCIA, Relative of missing migrant: "Look for him in the coyote arroyo near the border, where there's some fencing."
JEAN GUERRERO: A drug mule using Garcia's phone said he'd found the young man's body and phone in the Arizona desert. These men have volunteered to search for him.
We are now starting our search for Marco Antonio.
We drive into the desert, on our way to hike along one of the most dangerous smuggling routes near the U.S.-Mexico border.
MAXIMO GARCIA (through interpreter): If we find him, it's bad news for me. If we don't find him, it's bad news either way.
JEAN GUERRERO: The volunteers prepare their gear for hours of walking in 100-degree heat. They stock up on water and ice. They call themselves Aguilas del Desierto, or Eagles of the Desert.
They're plumbers, farmers, construction workers. Most are immigrants who live in San Diego. They spend their weekends rescuing migrants or recovering their bodies as far away as Arizona.
ELY ORTIZ, Founder, Aguilas del Desierto (through interpreter): So, their relatives will stop having uncertainty about, what happened to my relative to give them that peace.
JEAN GUERRERO: Founder Ely Ortiz started the group after his own brother, Rigoberto, disappeared trying to enter the U.S. through here in 2009. His coyote, or human smuggler, confessed he'd abandoned Rigoberto during his last breaths.
ELY ORTIZ (through interpreter): I would think, where's my brother? What happened to him? How did he die? A thousand thoughts went through my head. And I told myself, I'm not going to leave my brother lying out there.
JEAN GUERRERO: Ortiz called the Mexican consulates, Border Patrol and other agencies.
ELY ORTIZ (through interpreter): I asked everyone for help, and nobody would help me.
JEAN GUERRERO: So he went out on foot, with the help of human rights activist named Rafael Hernandez. Together, they found his brother's body. It was closure for the Ortiz family.
Inspired, Ortiz launched Aguilas del Desierto. He chose the name Aguilas because of the eagle's powerful eyesight and wingspan. His volunteers walk into the desert. Some stay with the cars to rescue us if necessary.
Ortiz reminds us not to lose sight of each other, for safety. Along the coyote arroyo, the earth is unusually fertile for a desert. It's one of the most transited border routes precisely because there's so much vegetation for cover. But that means it's also impossible to follow Ortiz's mandate to keep an eye on each other.
There's people to my left inside of the brush and to my right. Signs of migrants are everywhere, tossed Red Bulls, backpacks, dolls.
Here's a toy.
And drug mules' shoes with carpet strips on the bottom to cover tracks.
There are all over the place.
Most prevalent are these black gallon jugs, which smugglers sell as a sort of supernatural, strength-inducing water. I'm following a volunteer named Jose Genis. He says it's hard to spot bodies in this area because of all the foliage. Dying migrants often crawl beneath trees seeking shade.
JOSE GENIS, Volunteer: And it makes it difficult for us to find them because they kind of blend in, especially after a body has been decomposing.
JEAN GUERRERO: Genis is a Navy veteran and a licensed EMT. On previous searches, he has found dehydrated migrants trying to enter the U.S. illegally. He has helped save their lives, treating them until Border Patrol could come take them to the hospital.
JOSE GENIS: I feel American, but, at the same time, I have my roots from Mexico, so I try to help out as much as I can.
JEAN GUERRERO: The heat is oppressive, even through the trees. There are snakes and scorpions and cattle skeletons. We keep losing each other. We repeatedly have to stop and regroup, finding each other by blowing whistles. We have to make it out before sunset, when smugglers inhabit this terrain. But we're not covering nearly enough ground.
JOSE GENIS: If anything, we have one-and-a-quarter miles.
JEAN GUERRERO: We press on.
Genis and I find a Bible crawling with insects. I wonder if the person who dropped it made it out of this desert alive. Hundreds of people die crossing the border each year from things like dehydration or hypothermia.
In Arizona alone, the death count is astounding. Official figures exclude the countless bodies that are never found.
Ev Meade of the Trans Border Institute says border deaths since the 1990s range as high as 10,000.
EV MEADE, Trans Border Institute: Yes, this is a large number of people. And this is the kind of number we talk about when we talk about an armed conflict or a war.
JEAN GUERRERO: He says the deaths are linked to U.S. border fence construction. Border crossing deaths were almost unheard of until the U.S. built long stretches of border fence in the '90s.
Today, about 700 miles of the 2,000-mile border are fenced, mostly around cities. This has forced migrants onto remote, dangerous routes through the desert, with its extreme temperatures.
President Donald Trump has already signed a directive to start building a border wall.
PRESIDENT DONALD TRUMP: We're going to build the wall.
JEAN GUERRERO: Meade says Trump's wall could increase migrant deaths by funneling them onto still more dangerous crossing routes. Some are dying on the way.
EV MEADE: We just really haven't had a serious policy discussion or a public discussion about the humanitarian consequences of the building of the wall.
JEAN GUERRERO: Back in the desert, we pass barbed-wire fencing. Could it be the fencing referred to in the text message? Suddenly, someone finds something. I scramble up a hill, following Genis.
It might be him, but we don't know.
First, I see the skull. A few meters away are the legs, clothed in pants. The body has been torn apart by coyotes or some other animal. Genis says the body looks like it's been decomposing for about a month. Marco Antonio disappeared a month ago.
MAXIMO GARCIA, Volunteer (through interpreter): Unfortunately, we just found remains of a human being. We're going to investigate to see if it's him.
JEAN GUERRERO: Garcia calls his relatives to tell them what we have found. The Aguilas get to work. They can't touch the body. It could be a crime scene.
They note the coordinates of the remains, which they will share with local police. Officials will pick up the body and take it to the medical examiner for DNA analyses.
The men improvise a marker out of a balloon they find to help officials spot the body. Back at the vehicles, Garcia thanks the Aguilas for the search. He says they were the only people willing to help him.
For the PBS NewsHour, I'm Jean Guerrero along the U.S.-Mexican border.