Walnut Canyon has been rockfall-prone for centuries and millennia. What does that mean for those who center their activities in this valley?

The Ancestral Puebloans who lived in Walnut Canyon hundreds of years ago certainly knew the dangers of life in the Canyon. People who lived in the canyon year-round were familiar with the sound of falling rocks echoing through the canyon and may have been in danger.

However, this canyon has many other attractions, such as proximity to water, a great variety of natural resources, warm and cool microclimates, ease of shelter and construction in natural alcoves, and perhaps other attractions. It also had many attractions. And despite the dangers of living in such vertical environments, they have made the canyon their home for generations.

Two major rockfalls have recently affected the experience of visitors to Walnut Canyon. On December 7, 2007 (an infamous day), overnight, 49 tons of rock collapsed along the Island Trail, the main route into the canyon in Walnut Canyon National Monument, breaking benches and part of a railing. , rock fragments cascaded into the valley, exposing the ruins and shocking them.

The 49-ton rock itself, supported at one end by another giant rock, hit the Island Trail head-on, albeit fragile, and came to rest, completely blocking the island. This is due to a variety of reasons, including the complexity of removing such a large boulder, and stabilizing and restoring the trail on the narrow ledge of the steep switchback trail system 150 feet below the rim of the canyon. The trail will remain closed for the next nine months. .

Walnut Canyon and Flagstaff Regional National Monument resource managers developed the plan with input from trail crews at Glen Canyon National Park and Grand Canyon National Park, who mapped the rockfall areas. They decided to use an unusual technique to remove the rocks and avoid using explosives.

With trail switchbacks and ruins below, as well as a nearby Mexican barn owl habitat, blasting was undesirable. Extended demolition compound was used instead. It was a labor-intensive process of drilling a hole in the rock, pouring a liquid compound, and waiting hours for the compound to expand and break the rock.

During the first and most dangerous stages, the huge boulder fell and was unstable, so the Walnut Canyon trail crew did this while wearing safety lanyards attached to ropes. As the work progressed, workers from the American Conservation Experience (ACE), mostly foreign volunteer workers, used feathers and wedges to dislodge some pieces of broken rock into smaller pieces. Work was carried out to crush it into pieces of the size of building blocks. The manageably sized rock blocks were then assembled into an impressive 12-foot high retaining wall to further stabilize and protect the site.

This beautiful wall can now be admired along the Island Trail, about three-quarters of the way down the main steps.

Finally, we had to repair the trail, haul out the damaged concrete, pour in new concrete, and repair the railings, benches, and interpretive signs. ACE crew and Park Service personnel performed this work. After nine months of closure, Walnut Canyon’s popular Island Trail is finally open to the public again.

A former colleague of mine working at Walnut Canyon in 2008 documented many challenges involved in removing rocks and rebuilding trails. Interpreter ranger Steve Nycz took pictures every step of the process. A selection of these photos are reproduced here. Additional photos can be found in The Daily Sun’s online version of this column (search for “Janice Richmond” at azdailysun.com).

This is the first of a series of questions from two rangers about rockfalls at Walnut Canyon National Monument. The second column tells the story of a more recent rockfall (2015) and will be posted here next week.