Why are some Draper neighborhoods sliding? Robert Gehrke visits with a geologist to find out.

Scientists have studied landslides in the Draper neighborhood for generations. Some 55 have been mapped, but homes are still popping up.

(Leah Hogsten | The Salt Lake Tribune) The scene on Monday, April 24, 2023, where two homes located at 2463 and 2477 E Springtime Road collapsed into the adjacent canyon on Saturday.

Draper • The view is impressive from high atop Traverse Mountain — to the west is the southern Salt Lake Valley, and to the north Lone Peak, steep hillsides and rolling scrub oak.

On the surface, it’s little wonder so many people want to live here.

Developers are also rushing to erect high-end homes on the picturesque mountaintop — and why wouldn’t they, there are fortunes to be made.

It’s what’s under the surface — and has been for tens of thousands of years — that is the problem.

Since 1937, geologists have been mapping landslides in the mountaintop area that straddles the border between Salt Lake and Utah counties. Two decades ago, James McCalpin identified 55 landslides in the area. Fifteen were large, thousands of years old and considered to be largely dormant, but 40 were younger and more prone to slipping.

It’s an issue that scientists and Draper City leaders have been aware of for decades, but it became more pressing in the early 2000s when developers wanted to build the community of Suncrest.

After two homes slid into a ravine on the south slope of the mountain last month, I was curious about the potential for future problems. To be clear, we don’t yet know exactly why these homes collapsed — whether it was natural ground movement, poor design, faulty workmanship or something else entirely.

But I wanted to understand the dynamics better, so I spent an afternoon touring the hillsides with Salt Lake Tribune videographer Bethany Baker and University of Utah professor Kathleen Nicoll, who, in 2010, wrote about slides in Traverse Mountain and the potential problems they pose. Nicoll also takes her students on a field trip to the site to see how the earth moves.

What our visit to the community showed are the challenges in building homes meant to last generations on ground that continues to shift.

The signs of movement were practically imperceptible at first, but after a while, they became more apparent. At one spot she pointed to a large, older slide meeting a younger slide and pushing down the slope. Where the two slides meet, a retaining wall is bowed and a tree planted in the yard is bowed eastward to keep upright as its roots are being pushed west.

She showed us a spot where wooden guardrails along a sidewalk have been torqued enough that the railings are splitting and the heavy bolts holding them in have popped free. Cracks are developing between the sidewalk slabs. In one area, the rift has from 1.5 centimeters to 8 centimeters since she was here back in September.

Above that walkway, there is a row of homes that look like they couldn’t be more than a few feet from the steep slope. In 2005, the crumbling hillside forced crews to sink anchors into the ground and install netting to try to shore up the slope — but gravity appears to be winning the fight.

“Once there’s a landslide it tends to keep remaining active,” Nicoll said. “These can kind of go quiet but they probably aren’t dormant, so what we like to do as scientists is look for evidence that they’re moving.”

Large beams outside a few homes supporting roofs are clearly no longer vertical, the bases seemingly pushed away from structures, with visible cracks where they attach.

To show why this is happening, Nicoll took us along a popular trail to a silica pit where early settlers gathered the chalky, brittle rock to make glass. I picked up a chunk, squeezed it and it crumbled into tiny bits.

Nearby there was a section where the hillside had collapsed and flowed downhill, creating a small, undulating debris field ending in what is called a toe. This soft, disintegrating rock is all over this mountain and is the reason it is so prone to slide, Nicoll explained.

(Francisco Kjolseth | The Salt Lake Tribune) Robert Gehrke.

Later, standing outside the clubhouse at the South Mountain Golf Course, we are at the toe of another landslide. This one, the Little Valley Landslide, is massive and moved down the mountain an estimated 15,000 years ago.

“I feel that people should know all the aspects, because Utah is a place that has a lot of beauty and some places just might be more safe than others,” Nicoll said.

David Dobbins, the city manager for Draper City, said planners have been aware of the slide risk for years. In 2007, the city adopted a geologic hazard ordinance that requires potential developers to do technical studies in areas they intend to build.

The city then contracts with consultants to review the studies to ensure they’re complete. That was done in the Hidden Canyon area where the two Draper homes collapsed and the two sides went back and forth for months before the city approved the project.

Ultimately, Dobbins said, the city doesn’t have much leverage when it comes to dealing with developers. In 2010 the state Property Rights Ombudsman issued an opinion that, under laws passed by the Legislature, developers have a vested right to build. As long as the geologic study is complete and uses reliable data, the city has to approve the project and not engage in a protracted back-and-forth over the study’s adequacy.

Public records show the owners of both of the homes that fell into the ravine — as well as the neighboring homes that were damaged — received an assurance from the developer in 2021 that there was “No known geologic hazard” in the area. A year later, the city condemned two homes because they were unsafe.

So — here and the rest of the state — it is buyer beware. And sometimes that’s fine when the hazards are out in the open. But sometimes, they are just below the surface.

Tribune videographer Bethany Baker shot and produced the video in this story.