Those who were not immediately arrested remained on nearby Seep Ridge Road to "[make] sure that our comrades are not going to be abused by the police and make sure that they are being treated fairly," Lee told a reporter.
Another six were arrested while blocking the road and demanding their friends' release, according to the Facebook post by Peaceful Uprising, and late Monday afternoon, Utah Tar Sands Resistance tweeted that two more were arrested outside the Uintah County Jail, bringing the total number of arrests to 21.
"Uintah sheriffs used force to pull the protesters apart, and also targeted those providing media coverage. One protester is reported as injured," stated the Peaceful Uprising post. Activists said police canine units were also on the scene, including one dog that was unleashed, chasing protesters.
According to Lee, the action was staged in response to a June 12 letter sent to Calgary-based U.S. Oil Sands by the federal Environmental Protection Agency. That letter indicates that U.S. Oil Sands' project. which targets state-owned minerals, includes land within the Uintah and Ouray Indian Reservation.
"We have a lot of indigenous land defenders actually with us, including members of the Lakota and Dine [Navajo] tribes," she said.
Because the project impacts lands in Indian country, the tar sands mine and related processing facilities may need to clear additional regulatory hurdles administered by the EPA, which implements environmental programs on tribal lands.
U.S. Oil Sands has already obtained all the state permits required to begin construction on its 213-acre PR Springs site, which also has survived a challenge before the Utah Supreme Court.
The action comes as the culmination of a weeklong Climate Justice Summer Camp, which involved numerous climate and social-justice groups, including Peaceful Uprising, the Salt Lake City group co-founded by Tim DeChristopher.
Activists have been camped nearby on public land in the Book Cliffs since May, hoping to bring attention to what they say is destructive strip mining that could spread around the Uinta Basin should U.S. Oil Sands succeed.
The Utah School and Institutional Trust Land Administration, or SITLA, has leased 32,000 acres to the Canadian company for tar sands development, including 6,000 near PR Springs straddling the Uintah and Grand county line. Last month in response to the activist encampment, SITLA director Kevin Carter renewed a closure order, barring public access to any state trust lands for which applications for mining permits have been filed.
"We respect the right of these people to protest peacefully," said agency spokeswoman Deena Loyola. "However, their rights do not extend to trespassing and blockading equipment or law enforcement officials."
Utah Tar Sands Resistance has been maintaining a permanent "protest vigil" at a nearby BLM campsite known as PR Springs. They've been living there since mid-May in an effort to put a halt to tar sands mining in the Book Cliffs area.
Lee said that the protesters planned to remain at PR Springs indefinitely, and she invited the public to "come and participate, and observe what's going on."
In late June, the Utah Supreme Court threw out a challenge to the tar sands mine, saying Living Rivers, the environmental group that brought the challenge, was too late when it appealed the state groundwater permit given to U.S. Oil Sands.
The company has been clearing and grading the area for the last couple weeks, and the equipment being blockaded was used for that purpose, according to Lee.
U.S. Tar Sands officials were not immediately available for comment.