Monsoons triggered a falling boulder on U.S. Highway 160 west of Durango, backing up cars in both directions Friday afternoon.
The 4-foot by 4-foot boulder rolled down a hillside on the east side of the highway about 2:30 p.m. and landed on the edge of the eastbound travel lane. It rolled into the middle of the highway just east of the intersection with County Road 207.
No one was reported injured.
A trooper with Colorado State Patrol was on scene shortly after the boulder rolled onto the road.
Maintenance crews with the Colorado Department of Transportation used a loader to move the rock to a ditch. Department spokeswoman Nancy Shanks said crews will break the rock down into smaller pieces and move them away.
Shanks said its not uncommon for summer monsoons to trigger rockslides and mudslides on state highways.
Its time to start looking out for these rock incidents, she said.