Rebuilding a Tilting Overlook at Bryce Canyon’s Ponderosa Canyon Viewpoint

The stone columns at the Ponderosa Canyon viewpoint in Bryce Canyon National Park had been tilting toward the canyon for years, which made the area unsafe for visitors. Crews found out why when they took one apart, then rebuilt the viewpoint themselves. Jim Hall, the park's Chief, Engineer and Project Manager, wrote up the project for the National Park Service.

As the plateau rim weathers and erodes, it is not only hoodoos that change shape. All photos: NPS/Jim Hall.

A job usually contracted out

Most parks have maintenance crews that handle day-to-day problems, but few can do construction work that is normally contracted out. The project was first meant to involve the regional office, and then the park decided it could do it in-house after its Roads and Trails Foreman, who had worked at Zion National Park, arrived and brought the ability to manage skilled crews. The plan was to remove one tilting column to see how it had been installed, then work out how to stabilize the columns and replace the sidewalk and wooden barriers.

What the crew found

The columns turned out to be self-supported structures.

The columns were not connected to anything except the wooden barriers, unlike construction at the park's other viewpoints. Each one weighed approximately 1,600 pounds. Once the crew saw that a column could be lifted out, it removed the corner column too, for a full look at how the viewpoint was built. The author notes that a slab on grade had been poured up to the columns and the facing stones set with a thin layer of grout, and that it is remarkable none of this failed sooner. The side wall was a surprise as well: a mix of cinder blocks, smaller stone slabs and stone fascia, where such walls are usually made of large slabs.

The rebuild

1. Drill holes in the columns and epoxy in rebar so the whole area is tied together structurally.
2. Remove the sidewalk back to the existing curb and move the column positions in from the rim for stability.
3. Build formwork and rebar, then pour concrete with a step to carry the facing and curb stones, with contraction joints to prevent cracking.

Repouring the sidewalk and building the step.

4. Set the facing stones with epoxy rather than only grout, and grout between them. Winter moisture seeping into grout freezes and expands, which makes facing stones pop loose, and after repeated poppings they shift and begin to fail. The crew wanted to test whether a high-strength bonding adhesive would hold up differently in cold weather. The curb stones were grouted above.

Facing and curb stone installation.

5. Rebuild the small side wall with larger slabs after taking it apart.

Side wall repair.

6. Install the wooden barriers. The park gets logs from fallen trees in the park and from local outside sources. Each is cut to length and sliced so it rests on metal L channel that sticks out of the columns, then bolted. The crew coats them with linseed oil, usually 3 to 4 coats, which should last a few years before a refresh.

The result

The author writes that anyone who did not know the old viewpoint would never guess it had looked different, that the quality shows what the Park Service's craftsmen can do, and that their workmanship, if they are allowed to do it, most often exceeds what outside contractors provide for a fraction of the cost. With the safety concerns resolved, the park planned more minor repairs to give visitors a good view at this viewpoint.

Sources

• National Park Service, Bryce Canyon National Park article submitted by Jim Hall, P.E., Chief, Engineer/Project Manager: https://www.nps.gov/articles/000/ponderosa-canyon-viewpoint-repair.htm; rewritten in hubnx's own words.