Cannon Ball, N.D. – Late on Thanksgiving morning, as a mass of dark clouds gathered over the Standing Rock Sioux Reservation, young Lakota men on horseback galloped through a sprawling encampment that has become the site of a monthslong standoff over the 1,172-mile Dakota Access oil pipeline that runs from North Dakota to Illinois.

Weaving around smoldering campfires and tepees still covered with beads of frost, the men cried, "All women and children report to the dome! There has been confirmation of a raid!"

Within moments, a line of more than 200 women and children could be seen marching toward a large geodesic dome near the center of this encampment near the Cannonball and Missouri rivers. Once they arrived, a Lakota elder addressed the crowd. "If any one of you is afraid right now, then go home!" she said. "Leave." Not a single woman left. Even mothers swaddling infants stayed.

While the raid proved to be a false alarm, the incident is just one more sign that the swelling population at Standing Rock — which totaled 5,000 at last count — is digging in for a long, cold winter, even as federal and local officials prepare to evict them.

On Friday, the U.S. Army Corps of Engineers notified the Standing Rock Sioux Tribe that the land being used for the protests will be closed by Dec. 5, and, late Monday, North Dakota Gov. Jack Dalrymple ordered an emergency evacuation of the camp, citing safety concerns because of harsh weather. Both the Corps and the governor, however, said they had no plans to forcibly remove protesters.

The warnings have gone largely unheeded. Each day, more opponents of the Dakota Access Pipeline pour into the site, and many of the new arrivals are more defiant than those who came before. Protesters say the pipeline threatens clean water as well as areas considered sacred by Indians.

At a news conference Monday night, Phyllis Young, a Standing Rock Sioux spokeswoman, dismissed Dalrymple's evacuation order, saying "the governor has no jurisdiction in treaty territory." The Red Cross is being called in to help with medical issues at the camp, Young said. "We are prepared," she added. "We have lived here for generations under these conditions. This is Dakota territory."

Any attempt to clear the camp now, after seven months without a resolution, is likely to ensnare hundreds of women and children, which could inflame the already dangerous standoff, protesters warned.

"We know that if the women and children all leave, then it will be that much easier for the government to raid the site," said Meghan Green, 20, a college student from New Hampshire. "We can't afford to do them any favors."

This defiant tone prevails across what has become an impromptu community. A campsite that began in April with a few dozen praying protesters has swelled into a small city complete with dining halls, schools, free medical clinics, tea halls and art tents for children.

At night, the sound of hammers and drills from workers building small houses competes with the drumbeat emanating from the "sacred fire" at the center of the camp. A wooden shelter has already been designated for Mni Wiconi (which means "water is life"), the first baby born at Standing Rock. Marriage ceremonies are now a regular occurrence.

While American Indian elders enforce the rules, much of the grunt work has fallen to millennials and college students. At all hours of the day, young people are preparing meals in the mess hall, splitting wood and sorting donated clothing. In the evenings, they can be heard calling relatives from "Facebook hill," one of the few spots here with cell reception.

"Mom, it's about a pipeline!" one protester shouted into her smartphone. "It's about oil. It's about the environment. You just don't get it, do you?"

Shields and gas masks

The mood has grown increasingly uneasy since a violent standoff the night of Nov. 21. About 400 protesters and police faced off on a bridge that had been closed by authorities, blocking access to the pipeline site. Videos posted on Facebook show protesters being hosed down with water, even as nighttime temperatures dipped near 20 degrees. A 21-year-old woman from New York was seriously injured and underwent surgery in Minneapolis; her father said her arm was nearly blown off by a concussion grenade, a claim disputed by police.

Since the clash on the bridge, protesters have begun preparing for further confrontations. Volunteers overseeing the supply tents sent out urgent requests for more gas masks, mace and other protective gear. And at the camp's northernmost corner, a group calling themselves the "Red Warriors" have been carving plywood shields.

"Some may see this as a provocation," said a young woman, as she painted shields red. "But we have a right to protect our eyes and ears and arms from getting blown off, don't we?"

Others focus on a more obvious threat: the weather. With virtually no trees and just the distant hills to block the high prairie winds, the Standing Rock campground can grow bitterly cold at night.

Paul Sherlock, 55, of Cleveland, arrived three weeks ago and was shocked to see families squatting in tents meant for summertime camping.

"There is no way these will hold up in negative 20-degree winds," he said. With $30,000 borrowed on credit cards, Sherlock began hauling in trailers of lumber, nail guns and other building supplies. He now oversees a small army of young volunteers constructing up to a dozen permanent structures around the encampment.

"We just keep plugging people in," said Sherlock, his voice hoarse from working 17-hour days in the cold. "We're in a race against time to winterize this camp."

Prophecy?

The possibility of a quick or orderly resolution seems unlikely. Among the growing numbers of Indians arriving here from far and wide, many speak of the confrontation in epochal terms. They invoke an ancient Lakota prophecy, which says that a giant black snake will rise from the earth and bring devastation. For many here, the pipeline is the black snake.

On Thanksgiving night, Jesse "Jay" Taken Alive, former chairman of the Standing Rock Sioux Tribe, addressed several hundred tired protesters who gathered for a turkey dinner at the Standing Rock High School in Fort Yates, N.D. Among those in the audience was actress Jane Fonda, another in a series of celebrities who have embraced the protest.

In a speech that moved many to tears, Taken Alive compared the gathering of tribes at Standing Rock to the forces who supported Sitting Bull at the Battle of the Little Bighorn in 1876. "We must defend the women and children — and the water," he declared, as those in attendance raised their fists.

Matthew Vance, who lives in Topeka, Kan., and is of Cherokee descent, said tribes have come to view Standing Rock as "the last stand" of the Lakota people after more than a century of oppression.

Chris Serres • 612-673-4308