A Trump administration plan to build 25 miles of wall along a remote stretch of rolling grasslands and mountains in Arizona would block one of the largest and most important remaining wildlife corridors on the state’s border with Mexico, according to a report this month by the Center for Biological Diversity, a conservation group.
“A barrier here would block species movement, destroy protected habitats, and inflict irreversible damage on critical ecological linkages,” the report said.
Wildlife cameras have photographed 20 species of wildlife moving freely across the border in this area — including black bears, mountain lions and mule deer — movement that would be sharply curtailed by the planned 30-foot-tall wall, researchers say.
This part of the borderlands, which includes the San Rafael Valley and the Patagonia and Huachuca Mountains, also contains critical habitat for endangered jaguars, at least three of which have been recorded in the area over the past decade. At least 16 other threatened and endangered species are found there.
“It’s a good perspective of what’s going and what’s going to happen,” Gerardo Ceballos, an ecologist and a senior researcher at the National Autonomous University of Mexico, said of the report. If this wall and a few others are built, he said, “there will be no jaguars in the U.S. soon.”
The homeland security secretary, Kristi Noem, cleared the way for construction on this stretch of wall in June by issuing waivers that exempt contractors from more than 30 federal laws, including the National Environmental Policy Act.
Ganesh Marín, a biologist who studies wildlife movement with Conservation Science Partners, a scientific nonprofit group, said a border wall could also cause smaller prey animals to avoid the area. That, in turn, could lead to cascading negative effects within the ecosystem, according to a study that Dr. Marín published with John Koprowski, a researcher at the University of Wyoming.
The border wall doesn’t just prevent animal movement, Dr. Marín said, but “modifies the whole ecosystem around that community.”
In a time of drought, it’s especially important for large animals to be able to move long distances to find sustenance, which the border wall hampers, said Emily Burns, director of programs at Sky Island Alliance, an environmental group that monitors animal movements in the valley with a network of cameras.
The federal government had already built more than 220 miles of wall across Arizona’s southern border during the first Trump administration. Those 30-foot barriers consist of steel beams placed four inches apart, which halt most wildlife movement.
The border barriers in the San Rafael area now — low barbed wire fencing and chest-high vehicle barriers — allow animals to cross, according to Myles Traphagen, a researcher and coordinator with Wildlands Network, a conservation group.
Two nonprofit conservation organizations, the Center for Biological Diversity and Conservation CATalyst, filed suit on July 8 in United States District Court for the District of Arizona challenging Ms. Noem’s move to bypass environmental laws.
Some ability to waive federal laws to construct border infrastructure is granted by the Real ID Act of 2005, which helped the first Trump administration wall off much of Arizona’s southern border. Previous legal challenges to stop such activity have largely failed.
The Department of Homeland Security said in a news release that this new construction would help “impede and deny illegal border crossings,” without providing evidence of such activity in the San Rafael Valley. The department declined to offer additional comments for this article.
David Hathaway, the sheriff of Santa Cruz County, which extends into the valley, said illegal crossings were practically unheard-of in the area, which has no major roads for many miles in all directions and surveillance towers capable of detecting migrants.
U.S. Customs and Border Protection also declined to answer questions for this article, saying that such information “is the subject of ongoing litigation.” Before the lawsuit was filed, in early July, the agency told other publications that work was planned to begin “within 60 days.”
Mountains in the area, known as the Sky Island region, have unique biomes that shift as elevation changes, separated by expanses of valleys and flatlands. That variation contributes to making it one of the most biodiverse regions of the United States, with especially high diversity of birds, plants, mammals, reptiles and insects.
The San Rafael Valley and neighboring mountains have long been a place where animals have moved freely, as well as a source of grasses for basket-weaving and edible plants, said Austin Nunez, chairman at the San Xavier District of the Tohono O’odham Nation. He said he strongly opposed a wall there, in part because jaguars and bears are so revered in his culture. “It’s just a bad idea to put a wall up there,” he said.
Conservationists also expressed special concern about the effects of the wall on jaguars. For the cats to have a chance to repopulate southeastern Arizona, this corridor needs to stay open to wildlife, said Russ McSpadden, a conservation advocate at the Center for Biological Diversity who focuses on the Southwest.
Jaguars were breeding as far north as the Grand Canyon into the 1900s, but now the nearest known breeding population is in Sonora State, Mexico. Recently, male jaguars have been increasingly moving northward to reclaim old territory, including one individual photographed repeatedly from 2023 to 2024 in the Huachuca Mountains in Arizona that may still roam the area.
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