President Barack Obama made his first presidential visit to Indian Country on Friday – and some residents of the Sioux reservation used the opportunity to voice their opposition to a proposed pipeline that would carry tar sands oil through their land.

The president and first lady arrived by helicopter at the Standing Rock Sioux Reservation, which straddles the border between North Dakota and South Dakota. Native Americans, some dressed in full feathered headdresses and multicolored, beaded outfits, greeted the couple.

“We can follow the lead of Standing Rock’s most famous resident, Chief Sitting Bull. He said, ‘Let’s put our minds together to see what we can build for our children,” Obama said. Sitting Bull was a Sioux chief who defeated Gen. George Custer at the 1876 Battle of the Little Bighorn.

The Obamas also spoke privately with tribal youth about their challenges growing up on the 2.3 million-acre reservation, home to nearly 1,000 residents who struggle with a lack of housing, health care, education and economic opportunity.

Some Sioux leaders used the visit to tell Obama that the proposed Keystone XL pipeline — which would run through their land — would be a treaty violation.

Bryan Brewer, president of the Ogalala Sioux Tribe, said in a statement that the Keystone pipeline was “a death warrant for our people,” and that it would violate treaty rights. Critics of the pipeline warn of possible oil spills, environmental impact from the line’s construction, and Keystone’s overall effect on raising carbon emissions that spur climate change.

In April, Obama pushed his decision on whether or not to approve the pipeline further back, citing uncertainty over the planned route after a legal dispute in Nebraska over how its route there was approved. TransCanada Corp.’s controversial 1,661-mile Keystone XL pipeline would carry tar sands oil from Alberta province in Canada down to refineries along the Gulf Coast.

“We don’t want that pipeline running through our lands, we want protection of the water, of our health, we want protection of our homeland,” Standing Rock Sioux Tribal Council Representative Avis Little Eagle said.