A rock slide in Zion National Park that blocked both lanes of U-9 and closed a 15-mile stretch of the highway near Mt. Carmel Junction was cleared after about nine hours Thursday.

Chief Ranger Larry Van Slyke said two front-end loaders and three dump trucks moved 700 cubic yards of sandstone from the road. The debris had covered about 20 yards of roadway 10-15 feet deep near the eastern entrance of the mile-long tunnel.Some of the boulders had to be drilled and blasted before being carted away. Van Slyke said the road was reopened shortly before noon Thursday after engineers determined the road bed had been undamaged.

He also said the source of the debris - sandstone cliffs that had been blasted in road construction earlier this century - was assessed as safe, but he could not predict when the next slide would occur.

"It's just one of those things - it could be in the next five seconds or in the next five years," he said.