It is still unknown whether anyone was injured, said UDOT spokeswoman Melanie Buck. The cause of the slide is also unknown, though they are usually weather related, she said.
Crews closed the road west of Capitol Reef National Park, near Torrey, after the slide. It was reopened Tuesday morning for park visitors.
The slide occurred around 6:30 p.m. and buried a 350-foot strip of the road, about 5 miles east of the park's visitors center, Buck said.
The two-lane highway, which connects Hanksville and Richfield, could be closed for up to three days while crews clear the boulders, Buck said.
No similar incidents have been reported in the Wayne County park in recent years, Buck said. But rock slides have closed U.S. 189 in Provo Canyon twice in recent weeks.