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A look at the socioeconomic and environmental impact of a 2,000-mile long wall at the U.S.-Mexico border.

President Donald Trump’s promised border wall could cost between $10 billion and $60 billion.

Or more.

Or maybe a lot less.

It’s unclear how much of the border will get a wall, a fence or rely on technology and manpower.

It is clear Congress is girding for a fight over spending $1.6 billion on a project central to Trump’s campaign promises.

Such is the unsettled nature of the wall. Six months into Trump’s presidency, the “big, beautiful wall” he wants remains ill-defined and often seems a near-afterthought as the administration fends off investigations and struggles to find its legislative footing.

Still, the government is quietly proceeding with prototypes.

Honing in on the cost is difficult, primarily because Trump himself has offered shifting estimates and conflicting details.

This month, for the first time, he suggested that the nearly 2,000-mile border with Mexico could be secured with as little as 700 miles of wall. He has also variously suggested the wall could be 40 feet high or more. For now, the prototypes will be 18 to 30 feet high.

Engineers can design and rough out costs but critical details, such as its height, length and thickness, change the price tag by tens of billions. Then there’s the location.

“The major cost driver in this type of project is we are trying to build infrastructure in some of the remotest areas of the land,” said Barzin Mobasher, a professor of sustainable engineering at Arizona State University. “The idea of a wall of this magnitude has not been tried before.”

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Access to electricity, fuel, labor and other materials is limited, making it more challenging and more expensive, he said.

The budget demands of future congresses, Trump’s own political future and legal hurdles posed by political and environmental activists will also affect the project, said William Ibbs, professor of civil and environmental engineering at the University of California, Berkeley.

“Tell me all those political and social and environmental details, and…