NOGALES, Ariz. — Bulldozers and cranes are already shaping the San Rafael Valley as construction begins on one of the last unwalled stretches of the U.S.-Mexico border in southern Arizona. But as the 30-foot-high, 27-mile-long border wall takes form, conservation groups are pressing for urgent safeguards to preserve the region’s fragile ecosystem.

The $300 million project, led by Fisher Sand & Gravel Company under a U.S. Customs and Border Protection contract, began August 25 and is expected to continue until 2027. For many wildlife advocates, the timing underscores the urgency of ensuring that biodiversity is not sacrificed in the name of border security.

“Approximately 85 percent of the animals that encounter the wall are unable to cross — about nine out of 10 animals,” said Eamon Harrity, wildlife program manager for the Sky Island Alliance. “So the new wall will impact the region’s animals, such as coyotes, pumas, bears, wild boar, two species of deer, porcupines, coatis, rabbits, hares and jaguars.”

Harrity said his organization operates about 60 wildlife cameras in the San Rafael Valley and more than 125 across the Arizona border, documenting the movements of diverse species. He emphasized that without additional measures, many of these animals will lose vital migratory routes.

Currently, the wall design includes small openings — about eight inches by 11 inches — in some areas, as well as gates that open during seasonal rains. Wildlife advocates are urging CBP to make those gates accessible year-round and to incorporate more frequent crossings.

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“We designed a map with proposals for the best locations for wildlife passages, based on years of camera data,” Harrity explained. “Even small crossings greatly help species like coyotes and wild boars, but there are far too few — only about 40 across the whole region.”

The Sky Island Alliance and the Sierra Club are calling for wildlife crossings every quarter mile, which would create approximately 120 along the new stretch.

For advocates like Zach Palma, Mexico program manager for Sky Island Alliance, the stakes extend far beyond Arizona’s borders.

“Aside from expenses, the concerns are environmental damage and social division, and on the ecological side, this is one of the most important biocorridors in our region, the entire San Rafael Valley, where the crossing of many animals such as jaguars and ocelots, pumas, pronghorn and deer has been documented,” Palma said.

Construction is expected to move east from Lochiel toward the Huachuca Mountains and Patagonia, Palma added.

Meanwhile, Sierra Club border coordinator Erick Meza has raised concerns about the project’s water usage. He noted that contractors have already announced plans to extract millions of gallons from wells in Mexico for concrete mixing and road watering.

“We can expect the aquifer levels in the wells in Mexico to begin to drop during the wall construction; I can't tell you how much,” Meza said.

The wall’s development highlights the tension between national security goals and environmental stewardship. Advocates say the San Rafael Valley is not just another construction site but a critical wildlife corridor connecting species between Arizona and Sonora, Mexico.

For now, conservationists continue to push for modifications even as crews set up camps and install electrical systems to support the 100 to 150 workers on-site. With construction set to last several years, they say there is still time to ensure the wall does not irreversibly sever ecological lifelines.

Originally reported by Cesar Barron in Calo News.