Draper and Alpine officials along with geologists worry that building on parts of Traverse Mountain might mean developers are digging for disaster.
Preliminary geological mapping and research by the Utah Geological Survey two months ago found evidence of geological landslides — that vary from about 2 acres to more than 200 acres — in several places on the mountain where housing developments are proposed.
Gary Christenson, geologic hazards program manager for the Utah Geological Survey, said maps show evidence of past landslides in Draper, which crosses the mountain into Utah County, one near Micron, one in Lehi near Point of the Mountain, and another near Fort Canyon in Alpine.
Christenson said geologists don’t know how long ago the movement might have caused the slides, but he estimates around 10,000 years ago. There is some concern that development, regrading, earthquakes and the introduction of water on the mountain could cause the land to move again, he said.
“It is possible to reactivate a dormant landslide because you could be changing the stability of the mountain.” Christenson said
The early findings were sent to the cities that might be affected a month ago. When past landslide activity is detected most cities require developers to hire their own geologists and investigate the land further, Christenson said.
Draper is in the process of investigating the mountain because of a proposed housing development by SunCrest. Lehi has already determined that Traverse Mountain development would not be affected, and Alpine is still investigating. But landslides are hard to predict and may not have any movements for hundreds or thousands of years, Christenson said.
“You have to predict what’s going to happen, which is very hard to do,” he said. “There is a great deal of uncertainty and very little that you ever know for sure.”
If a landslide occurred, it would most likely be a gradual elevation change with the homes cracking and being displaced, not necessarily houses rolling down the mountain, he said.
Development on the mountain, with regrading to build the homes, can have negative and positive effects. Regrading on top of an existing landslide could ease the burden on the land beneath.
But if the developers cut into the middle of an existing landslide, they could destabilize the land beneath and activate the slide, Christenson said.
Draper city officials aren’t taking any chances. A geological hazards ordinance already is in the works that may require developers to tell potential homeowners about possible geological hazards or have a risk threshold that still allows people to build, said Pete Shabestari, geographic information systems manager for Draper city.
Geologists are investigating to see what the landslides could mean, and the ordinance would simply get ahead of the problem.
“We don’t want to say you can’t build, but people must know and be comfortable with a certain level of risk,” Shabestari said. “We just want to be more proactive so people don’t find out about a possible problem after the fact.”
Alpine already has a geological hazards ordinance and a hillside ordinance that requires builders to map and have geological tests. City officials could deny a building request if they think the mountain is unstable, Alpine city administrator Ted Stillman said.
Requests were not denied more than 10 years ago when homes were built near Preston and Willow Canyon in Alpine. At the time there were no ordinances for building on the mountain, and now a debris basin must be created on the mountainside to save homes from mudslide damage. The residents must raise the money for the debris basin excavation.
A development in its early stages on the north end of Fort Canyon is going up the mountain, and city officials are making certain that more geological tests are done, Stillman said. He was not surprised about the slides the geological survey found.
“It’s always been a concern because everyone knows the Wasatch Fault runs right through there, so we knew we were going to have to look at the mountain closely,” Stillman said.
And that is what the city is requiring developers to do.
The development, with a tentative name of Three Falls, will go to the planning commission with a more detailed concept plan on Dec. 2, and then to the City Council, Stillman said.
When a group of Lehi officials went out to Lehi’s section of the mountain with the geological survey two weeks ago, they apparently found nothing that would stop construction on Traverse Mountain, Lehi city engineer Lorrin Powell said. But he hasn’t received the full report from his staff yet.
The city required a geological technical report from developers before construction began on the Traverse Mountain development.
There are two developments near Point of the Mountain –Traverse Ridge in Draper and Traverse Mountain in Lehi. SunCrest Development is building the homes in Draper, and when completed — at least two years from now — the development will include 3,800 homes on the Utah County side of the mountain, said Ty McCutheon, vice president for SunCrest.
Having geologists come and survey the land is not uncommon for the company, he said.
“Every time we go into a new neighborhood we do extensive studies,” McCutheon said. “I think it goes to back what the science tells you, and in every state every piece of land has unique characteristics. We just try to understand what’s going on and then we make modifications.”
Elisabeth Nardi can be reached at 344-2547 or firstname.lastname@example.org
This story appeared in The Daily Herald on page C1.