Protesters against the Dakota Access oil pipeline briefly blocked two entrances to a pipeline work yard in a rural North Dakota town early on Saturday morning, causing workers to leave the area, police said.

Morton County Sheriff’s Department spokesman Rob Keller said law enforcement received a call at around 9 a.m. (CST) telling them a caravan of between 130 and 150 cars, each carrying three to four people, left the protest camps and headed north to the city of Mandan where equipment is located.

“They went west for a few miles (from there), they turned on that road that leads to the Mandan landfill and that’s where the North Dakota pipeline have equipment,” Keller said. “It’s their work yard.”

The latest demonstration took place just a day after nearly 40 people were arrested on Friday at the construction site for the pipeline, which has drawn opposition from Native American and environmental activists since the summer.

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Shortly after 10 a.m. (CST) on Saturday, pipeline workers evacuated the work yard while the protesters blocked its two entrances, Keller said. Law enforcement officers arrived on the scene and monitored what they said was a peaceful protest until about 12:15 p.m. (CST), when the protestor left the area.

Keller said no arrests were made and that there was no information on any injuries, despite a report saying one protester was hurt.

“We cannot verify that there was a woman who was injured,” Keller said. “Once she found out the ambulance was on the way she said she didn’t want to go to the hospital, so they stopped the ambulance.”