PIERRE, S.D. (AP) — A federal board's Thursday decision to rename Harney Peak to Black Elk Peak surprised South Dakota's governor, but vindicated activists who unsuccessfully argued to state officials last year that the peak shouldn't bear the name of a man whose soldiers killed Native Americans.

The decision by the U.S. Board on Geographic Names will cause "unnecessary expense and confusion," Gov. Dennis Daugaard said Thursday in a statement. The governor said he's heard little support for renaming the peak, which is South Dakota's tallest and stands in the Black Hills National Forest.

"I suspect very few people know the history of either Harney or Black Elk," Daugaard said in a statement.

Black Elk was a Lakota spiritual leader who died in the mid-20th century.

"He's definitely a very powerful visionary that is at least deserving of the peak's name," said Wayne Frederick, a representative on the tribal council of the Rosebud Sioux Tribe in southern South Dakota. "It's extremely uplifting."

Frederick said he was in a council meeting all day, and when he learned of the change, he passed his phone around to several representatives near him. "They were in disbelief," he said.

The federal board determined from the input received that Harney Peak was concerning to Native Americans in the area, said Lou Yost, the board's executive secretary for domestic names. The vote was 12 in favor, none against and one abstaining, he said.

"In this case, the board felt that the name was derogatory or offensive being that it was on a holy site of the Native Americans," Yost said, adding that the change applies to federal usage on new maps or other products.

Army Gen. William S. Harney's men massacred Native American women and children during a battle in September 1855, according to historic records.

Some people last year argued to the state's Board on Geographic Names that Harney Peak was offensive and should be changed, but the board decided against backing a new name. Members of Daugaard's administration opposed efforts to have the name changed, and state lawmakers eventually approved a law in 2016 that limited the board's autonomy.

Republican U.S. Sen. John Thune said in a statement that the federal board's "unilateral" decision is upsetting and "defies logic" since it goes against state officials' recommendations.

Basil Brave Heart, a member of the Oglala Sioux Tribe, proposed the change to Black Elk Peak. Brave Heart didn't answer a telephone call for comment Thursday.

"I don't want to see a peak that's named after someone that violated women and children," Brave Heart said in 2015. "Our people had to live under that icon, that man who did that to our people."