"Southern Border Wall: Campaign Slogan Meets Reality"

RACHEL MARTIN, HOST:

Donald Trump talked a whole lot about building a wall between the U.S. and Mexico when he was a candidate. Now that he's president, it's unclear just what that wall is going to look like and when it might get built. What we know so far is that it's likely to be a fence, not a wall. It won't extend the length of the border, and it will be very unpopular with our southern neighbor. NPR's John Burnett reports.

JOHN BURNETT, BYLINE: At the moment, about a third of the 2,000-mile border with Mexico is fenced. There are three kinds of fencing - some 10 feet tall, some 20 feet, some wire mesh, some steel posts. You can see all three types here in the gritty, no man's land between Tijuana, Mexico, and Imperial Beach, Calif. This is the oldest.

(SOUNDBITE OF KNOCKING ON METAL)

JAMES NIELSEN: This fence that I just struck is landing mat material from the Vietnam War.

BURNETT: James Nielsen is a Border Patrol agent in the San Diego sector.

NIELSEN: And we use it as our primary fence, which is a vehicle barrier so vehicles wouldn't easily be able to drive from Mexico into the U.S.

BURNETT: Border enforcement officials have been telling Trump's transition team that a fence alone is not enough. You also need agents, camera towers, stadium lights and sensors. If the president insists on a great wall to deliver on his signature campaign promise, Customs and Border Protection has identified 400 miles where the fence can be extended or reinforced. But there are clearly sections where it remains impractical. For instance, the border fence stops at a gnarly mountain range at Otay Mesa, about 15 miles east of the Pacific Ocean. The view from here is open country - no dividing line, no nothing.

Again, Agent James Nielsen.

JOSHUA DEVACK: At the time that this fence was built, it was too expensive to continue. And there's also this natural barrier here that a lot of crossers choose not to climb this mountain. They prefer to have easier access to roads and civilization.

BURNETT: According to an 8-year-old estimate by the Government Accountability Office, the border fence cost the government $3 million to $4 million a mile to build. Estimates for additional fencing in harsher terrain could surpass $10 million a mile. Trump still claims he'll give the bill to Mexico. Earlier this month, Mexican President Enrique Pena Nieto restated that his country, of course, will not pay. The existing wall and talk of more wall remains unpopular with Mexicans.

As the border agent is interviewed, a 15-year-old Mexican girl named Carla Martinez watches from a park on the Tijuana side. I thrust a microphone through the narrow space between the thick iron posts.

(Speaking Spanish).

CARLA MARTINEZ: (Speaking Spanish).

BURNETT: "We're against it," she says. "We won't pay for it. It's bad because it's racist. There has to be a border between different countries. But this is just going to divide us more."

CARLA: (Speaking Spanish).

BURNETT: Mexico has not made the fence-building easy. In the mid-2000s, a company called Sundt Construction erected about a hundred miles of fence in the remote West Desert. Company president Mike Hoover says the U.S. government told his construction crews not to set foot across the international divide.

MICHAEL HOOVER: So we had a tight working area. That was a challenge. It was unusual. But with proper planning, we could work our way through that.

BURNETT: There were other challenges. In one stretch near Yuma, Ariz., the soil was so soft they had to tow their equipment in with bulldozers. In some places, they had to blast through solid rock to set the fence panels. Summer temperatures soared above 100 degrees. Workers had to take frequent breaks to avoid heatstroke. And because some Mexicans were hostile to the fence, Hoover says federal border agents and private security guards had to protect his construction crews 24/7.

HOOVER: We did have some instances of rock-throwing from the Mexican side. I know of at least one instance where we had some shots fired in our direction, close enough that we were plenty worried.

BURNETT: Despite the challenges, if Trump gets his wall Sundt Construction hopes to win a new contract and return to the border to continue the international fence.

John Burnett, NPR News, Chula Vista, Calif.

[POST-BROADCAST CORRECTION: In the audio, the following quote should have been attributed to Border Patrol spokesman Joshua Devack, not agent James Nielsen: “At the time that this fence was built, it was too expensive to continue. And there's also this natural barrier here that a lot of crossers choose not to climb this mountain. They prefer to have easier access to roads and civilization.”]