Standing Rock encampment near Cannon Ball, North Dakota

CANNON BALL, NORTH DAKOTA – DECEMBER 4: Sioux Chief Arvol Looking Horse, spiritual leader of the Seven Council Fires, arrives at the Sacred Circle to announce that the US Army Corps of Engineers will no longer grant access to the Dakota Access Pipeline to put their pipe line on the boundary of the Standing Rock Sioux Reservation at Oceti Sakowin camp on December 4, 2016 in Cannon Ball North Dakota, Colorado. Native Americans and activists from around the country have been gathering at the camp for several months trying to halt the construction of the Dakota Access Pipeline. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Helen H. Richardson/The Denver Post via Getty Images)