Work on a $10 billion project that will funnel renewable energy across the West has come to a halt in southwestern Arizona, with Native American tribes saying the federal government has ignored concerns about effects that the SunZia transmission line will have on religious and cultural sites.

Federal land managers temporarily suspended work on the SunZia transmission project along a 50-mile (80-kilometer) segment last week after the Tohono O’odham Nation asked for immediate intervention, saying bulldozers were clearing a stretch of the San Pedro Valley and that one or more historic site were demolished.

The tribe was joined in their plea by the San Carlos Apache Tribe and archaeologists. Zuni Pueblo in neighboring New Mexico and other tribes in the Southwestern U.S. also have raised concerns, saying the area holds cultural and historical significance for them as well.

The letter includes a photograph of an area where desert scrub was cleared in preparation to build pads for transmission line towers along with hundreds of miles of access roads through a valley that tribal officials and environmentalists say is relatively untouched.

Renewable energy advocates have said the SunZia project will be a key artery in the Biden administration’s plan for boosting renewables and improving reliability among the nation’s power grids. It will stretch about 550 miles (885 kilometers) from central New Mexico, transporting electricity from massive wind farms to more populated areas as far away as California.

Pattern Energy, the developer, has billed the SunZia project as an energy infrastructure undertaking bigger than the Hoover Dam. Executives and federal officials gathered in New Mexico in September to break ground on the project.

Verlon Jose, chair of Tohono O’odham Nation, suggested in an Oct. 31 letter to the Bureau of Land Management that the agency was prioritizing SunZia’s interests rather than fulfilling its trust responsibilities to tribes.

He pointed to an order issued by U.S. Interior Secretary Deb Haaland that calls for federal land managers under her direction to “give consideration and deference to tribal proposals, recommendations, and knowledge that affect management decisions on such lands.” Haaland is a member of Laguna Pueblo in New Mexico.

“We hope you will agree that bulldozers are poor tools for consultations or for treating places having exceptional significance in O’odham, Apache, and Zuni religion, culture, and history,” Jose wrote.

Bureau of Land Management Director Tracy Stone-Manning said in a letter to Jose last week that she was asked by Haaland to respond to the concerns. She suggested having a meeting in the coming days.

The agency did not immediately respond to an email message from The Associated Press asking about the tribes’ concerns. It was also unclear how long the work would be suspended.

Pattern Energy said Monday that it considers the pause on work as “a good faith step” as part of the Bureau of Land Management’s consultation process.

Natalie McCue, Pattern Energy’s assistant vice president for environmental and permitting activities, said the company has worked to address tribal concerns over the years and that the transmission line will be parallel to existing infrastructure within the valley to minimize the impacts.

More than a decade in the making, SunZia’s line would be capable of transporting more than 3,500 megawatts of new wind power to 3 million people in the West. In New Mexico, the route was modified after the U.S. Defense Department raised concerns about the effects of the high-voltage lines on radar systems and military training operations.

Environmentalists also were worried about impacts on wildlife habitat and migratory bird flight patterns in the Rio Grande Valley.

There are similar ecological concerns in the San Pedro Valley. The transmission line is at the heart of a legal challenge pending before the Arizona Court of Appeals over whether state regulatory officials there properly considered the benefits and consequences of the project.

Pattern Energy officials said the company will be planting about 10,000 agave and 7,000 saguaro cactuses as part of restoration efforts and will be funding a plant salvage study as well as work to identify new agave species along the San Pedro River.