Rick Bowmer, AP
This July 13, 2015, photo, shows construction at the U.S. Oil Sands commercial tar sands operation, in the Book Cliffs, in eastern Utah. Utah state officials have given the go-ahead for the mine under construction the eastern flank of the state, but they will require the company to do water and air quality monitoring in a move environmentalists are calling a victory. (AP Photo/Rick Bowmer, file)

SALT LAKE CITY — Four protesters attempting to occupy land leased to U.S. Oil Sands in Uintah County on Monday were arrested and booked into jail, police said.

Amber Hayward, Tazeus Steyskal, Jay Brooks and Sean Summers are being investigated for suspicion of trespassing on trust lands, a class A misdemeanor, the Uintah County Sheriff's Office said. The environmental activists were on the property in the remote Book Cliffs area of the county on behalf of Peaceful Uprising, an environmental advocacy group.

Some of the protesters perched atop steel tripods on the property, which made it difficult for them to be removed, police said.

"Heavy equipment was utilized to remove a female from her tripod, after which another person chose to attach himself to (that) heavy equipment," the sheriff's office said in a news release. "He was eventually removed, and both subjects were arrested. During that operation, one subject repeatedly entered onto the restricted property to bring items to and speak with the female on the tripod, despite being asked and warned not to. He was arrested. A second protester was then removed from atop his tripod and arrested."

Peaceful Uprising provided updates about the protest and arrests throughout the day on its website. The group opposed U.S. Oil Sands' use of the land for mining, saying it will severely harm the environment of the Upper Colorado River Basin.

“U.S. Oil Sands continues (the) sick tradition (of exploitative mining) by squandering precious water in a thirsty region and saddling future generations with a toxic legacy there is no way to clean up,” Melanie Martin, a spokeswoman for Peaceful Uprising, said in a prepared statement.

The advocacy group said bail was set at $3,900 for each of the protestors arrested and made a plea for outside help in obtaining their release.

"We're currently negotiating terms of a bond as we can not pay that $15,600 cash bail," reads a statement on the organization's website.

The Uintah County Sheriff's Office said the protestors would not have been arrested if they had not trespassed on private property and refused to leave.

“Peaceful protests respect the rights of others with as much reverence as their own," said sheriff's Cpl. Troy Slaugh in a statement. "Unfortunately in this case, some chose to express their beliefs in a way that interfered with others being able to go to work and earn a living, and they trespassed on a private entity’s property, essentially forcing our hand.”

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