The Big Bend project planned for southern Minnesota would be one of the state's biggest wind farms, and paired with a large solar plant, would be different from any other power project in the state.

But Big Bend's proximity to the Jeffers Petroglyphs site — sacred to Indigenous people — has alarmed the state's historic preservation office and the Lower Sioux Indian Community.

"I just want to emphasize that to the Lower Sioux this project is considered a high priority," Cheyanne St. John, the tribe's historic preservation officer, told Minnesota utility regulators Thursday. "This site is highly significant to the Upper Sioux and Lower Sioux (communities), but also to tribes that are out of state as far as Missouri."

The Minnesota Public Utilities Commission (PUC) on Thursday accepted Big Bend's application for review, but the Jeffers Petroglyphs issue will get special scrutiny before any approval of the project.

The Jeffers Petroglyphs, near Comfrey, Minn., are a collection of about 5,000 rock carvings listed on the National Register of Historic Places. The carvings date back 7,000 years and are considered sacred to tribal nations, including the Dakota, Cheyenne, Ioway and Ojibwe.

Tribal members "actively continue to pray and hold ceremonies [at the petroglyphs], as their ancestors have done for thousands of years," the Minnesota Historical Society said in a PUC filing.

The Big Bend project, which is being developed by Apex Clean Energy Holdings, would entail about 55 wind turbines that could produce up to 308 megawatts of electricity.

Big Bend is linked to Apex's nearby Red Rock solar project, which would have up to 60 megawatts of power production capacity.

Apex's proposal also calls for an 18-mile, 161-kilovolt transmission line to connect Big Bend to the grid. Together, Big Bend and Red Rock would constitute the first large wind-solar hybrid project in Minnesota.

The Minnesota Historical Society, which runs the site, argued in a filing that adding wind turbines to the petroglyphs' "view shed" would "dramatically diminish the integrity of the property's significant historic and sacred features."

After hearing the complaints, Apex moved the wind turbines nearest to the petroglyphs from just over 2 miles to 5.2 miles away.

But the historical society and the tribes want an 8-mile buffer, and they object to Apex's decision to significantly raise the height of the turbines along with the move.

"It is still falling short for us, to be blunt," Kevin Maijala, the historical society's senior director of learning initiatives, told the PUC Thursday. "We really are at an impasse in regard to the impact."

Christina Brusven, a Frederikson & Byron attorney representing Apex, told the PUC the project is "hemmed in" to the east by a military flight path. And to the south, Big Bend is limited by the presence of other large wind farms.

In an interview, Apex spokesman Max Jabrixio said the taller turbines are needed because of the increased setback to 5.2 miles.

Essentially, Apex removed the towers closest to the petroglyphs from its plans, but then needed to increase the energy production of the remaining towers to compensate for that move, he said. Taller towers with bigger blades allow for that.

The PUC referred the petroglyph issue to a "contested case" hearing before a state administrative law judge.

Mike Hughlett • 612-673-7003