The Wild Horse Stampede is a big deal in Wolf Point, Montana. The oldest rodeo in the state, the annual Stampede draws thousands of equestrian enthusiasts to the town of 3,000.

But while visitors rushed into Wolf Point for the 2013 Wild Horse Stampede, some residents were allegedly pushed out. To clear the streets for 2013’s wave of horse-happy tourists, Wolf Point law enforcement led a raid on local Native Americans, illegally detaining them without charges or toilets in a makeshift outdoor jail, members of two area tribes allege in a new lawsuit (PDF).

Wolf Point locals refer to the arrests as the “Wino Round Up.” The name derives from an area slur against Native Americans.

Located on the 2 million-acre Fort Peck Indian Reservation, the city of Wolf Point is home to local Assiniboine and Sioux tribes, as well as a non-Native population, and a city government and police force unaffiliated with the reservation.

Relations between Wolf Point government and the tribe members are sometimes strained, the plaintiffs say. Elected officials and police officers frequently dismissed this group as “Homeless, Winos, Street People, Tree People, Drug Addicts, Alcoholics, or Prairie Niggers,” members of the Fort Peck tribes allege in their lawsuit.

Most days, Wolf Point is roughly 40 percent white, 50 percent Native American, according to 2010 census data. But when the Wild Horse Stampede rolls around every second week of July, the town’s demographics see a sharp swing. The event, which boasts “thousands of attendees” is a “largely a white Anglo-Saxon event,” the lawsuit reads. (Wild Horse Stampede promotional materials encourage visitors to try the rodeo’s “Catholic burgers, another Stampede ritual served by the local Catholic parish and a few Lutherans.”)

Shortly before the 2013 Stampede, Wolf Point officials launched a one-day arrest spree, which the plaintiffs say was meant to make the city appear even whiter. The city denies this claim.

“To sensationalize this story and twist it into a white versus Indian issue is irresponsible,” Wolf Point City Attorney Anna Rose Sullivan told The Daily Beast. “Such misconceptions contribute to the chasm that has been forced between races and ultimately between each individual person.”

Sullivan noted that the arrests had been carried out in part by tribal executives and police, some of whom are named in the lawsuit.

But the plaintiffs offer a less-rosy account of events. In pre-rodeo sweep on July 12, 2013, they say, local police cracked down on the people they had described in such unsavory terms: the homeless, “wino,” and drug-addicted members of the city’s Native American community.

Police, some allegedly wearing masking tape over their badge nameplates, “removed 30 to 50 individuals to curb the American Indian presence,” the lawsuit reads. But city arrest records show no sign of the raid; the arrested parties, more than 30 of whom are suing the Wolf Point police and mayor, say they were never served official charges, never read their Miranda Rights, and never allowed to meet with lawyers. Instead, they describe a period of unlawful detainment, during which they were denied basic legal aid or health facilities while the Wild Horse Stampede festivities kicked off.

With a population just under 3,000, Wolf Point is ill-equipped to handle the mass arrest of 30 to 50 people. When the police force ran out of squad cars and paddy wagons, they improvised, packing the Native American detainees into “vehicles which were not adequately vented,” the suit reads, causing at least one person to lose consciousness.

The jails were similarly overwhelmed. With their cells full, police allegedly began housing detainees on two outdoor basketball courts: men on one court, women on the other. There were no toilets, no medical facilities, and no protections against the elements.

“Women were provided a blanket and a pot in which to relieve themselves,” the plaintiffs write. “Men were instructed to urinate through the fence. Some of the male plaintiffs will testify that they were unable to get near the fence and so were forced to ‘pissed or shit their pants.’”

The first day was excruciatingly hot; causing at least one person to faint. The night was worse. Faced with a “sudden and violent rainstorm,” police attempted to place tarps over the basketball courts. When the makeshift tents failed to protect the detainees, police allegedly moved them off the courts, to “even tighter confinement within a windowless garage.”

Eventually, over the course of the following day, the detainees say they were released. But multiple have subsequently died, “their deaths accelerated or caused by the physical stresses experienced during the incarcerations,” the lawsuit claims.

The city says these claims are baseless.

“Our office cannot comment on the specifics of pending litigation against the City of Wolf Point or Roosevelt County,” Sullivan told The Daily Beast. “I can only say that these allegations have no merit and we are confident that our police officers, sheriff’s department, mayor, and town council will be vindicated by the ultimate outcome in this case.”

But a partially redacted internal investigation, obtained by Montana’s Great Falls Tribune, suggests a deliberate effort by police to detain the city’s Native Americans without charges.

“On April 15, 2014, IAD (Internal Affairs Division) interviewed Lieutenant (name deleted),” the report reads. “Lt. (name deleted) proffered that the corrections officers were told that they would be detaining the ‘street people’ for twenty-four hours. Lt. (name deleted) advised that she protested that this was wrong, that holding these individuals without formally charging them would be violating their civil rights. Lt. (name deleted) asserted ‘I knew this would come back and bite everyone in the ass.’”

Meanwhile, the Wild Horse Stampede has thundered on without a hitch: In 2015 it won the Women’s Professional Rodeo Association’s “Small Rodeo of the Year” award.

“The Wild Horse Stampede offers a glimpse of unadulterated eastern Montana life. There’s no glitz. Just honest-to-goodness fun based upon decades-old traditions,” the Wolf Point city website boasts. “It’s the Montana rodeo other seeks to emulate.”