An overnight rock slide in Zion National Park blocked both lanes of U-9 and closed a 15-mile stretch of the road west of the mouth of Caramel Junction.

Chief Ranger Larry Van Slyke said the slide covered about 20 yards of roadway with debris near the eastern entrance of the milelong tunnel.The boulders, including some which had to be drilled and blasted before being carted away with front-end loaders, were 10-15 feet deep on the roadway. Van Slyke said crews were working to clear the debris, and he expected the road to reopen by nightfall.

The slide occurred in a rock cut that had been blasted when the road was built years ago, and Van Slyke said there was no recent rain or snow that would have triggered it.

"That's part of Zion Canyon country and part of canyon country life," he said. "These rock falls commonly occur in Zion."

Traffic on the road had been increasing in recent weeks, and Van Slyke said about 60 oversized vehicles were escorted through the tunnel on Wednesday.

During a typical day during the peak in July, Van Slyke said about 150 vehicles are escorted through the tunnel, and on some days more than 200 vehicles are taken through.