Blast removes rock slab above Timpanogos Cave trail

HIGHLAND — A single, resounding blast echoed off the walls of American Fork Canyon as tons of rock were sheered off the cliff above the Timpanogos Cave National Monument trail.

"Dang, that sounded good," said a woman's voice over the National Park Service radio frequency.

The blast removed a 30-foot-long slab of rock that hung precariously above a shelter built at the cave's exit. The slab was about 2 feet high and 4 feet deep.

The explosion was powerful enough to shake the snow off the roof of the shelter, which has protected cave visitors for decades from rocks that occasionally tumble down the steep mountainside.

When cave managers decided to rebuild the shelter this year with funds provided by the American Recovery and Reinvestment Act, experts evaluated the cliffs above the shelter and found a 4-inch gap between the cliff and part of the rock slab.

The gap was substantial enough to make the experts think it threatened the cave exit shelter and also some power poles, said Karissa DeCarlo, a spokeswoman for Timpanogos Cave National Monument.

DeCarlo said officials decided to remove the slab before the cave opens for visitors May 9. The shelter will be rebuilt this summer and the exit trail rerouted to avoid areas prone to rockfall. Construction shouldn't affect cave visitors, park officials said.

A crew of three demolition experts, two from Canyonlands National Park and one from Rocky Mountain National Park in Colorado, oversaw placing the Kinepak explosive to remove the slab — a process that required mountain-climbing skills and took a good part the day. The blast originally was planned for Wednesday but was moved up a day to avoid bad weather.

Traffic along U.S. 92 through American Fork Canyon near the cave was stopped for the blast, but no debris could be seen tumbling down the mountain following the blast. Once the dust cleared, a dark scar on the cliff face marked where the slab had been.

"I'd say that's a success," DeCarlo said.

Timpanogos Cave is one of Utah County's most popular attractions, with 80,000 people hiking the trail to tour the cave last year and 120,000 coming to the visitors center.

It is common for rocks to fall on the 1.5 mile trail from the visitors center to the cave entrance, but they seldom hit anyone. DeCarlo said one person was killed on the trail in 1933. It's the only known rock-related death at the park.

e-mail: mhaddock@desnews.com