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Active rock slides at Dinosaur National Monument have closed Jones Hole, an area popular with hikers and anglers on the monument's Utah side.

Trouble began Tuesday morning when a cliff over Jones Hole Creek dropped a modest slide. The spot is near the Colorado state line just inside the park's north boundary at the Jones Hole Fish Hatchery and trailhead.

Thursday morning saw a repeat performance, followed by a much larger event at noon.

"It sent boulders down as big as pickups," said Dan Johnson, Dinosaur's chief of interpretation and visitor services, who has posted photos. "The outer layer is exfoliating. There is a potential for a lot more rock fall. It seems to be happening in the mornings when the sun heats it up."

This last slide, which broke trees and sent boulders across the creek and the trail beside it, prompted Superintendent Mary Risser to close the slide area until further notice. Also closed is the 4-mile trail that follows the creek from the hatchery to the Green River. No one has been injured although a fisherman had to run to avoid being struck by a rock as it crashed into the creek.