ROCKVILLE, Washington County — The Utah Geological Survey says the area where a massive rock fall killed two people last December remains so dangerous it is recommending Rockville move people out and raze any remaining structures.
A geologic investigation into the Dec. 12 massive event in which a rock mass of about 2,700 tons fell concludes the likelihood of another rockfall in the area is "very high" and that precautionary steps should be taken.
"In our estimation this has moved beyond the 'thinking about it' stage," said William Lund, senior scientist with the survey over geologic hazards.
"There are some geologic hazards that are an annoyance and there are those that are deadly," he said, adding that the western half of the little Zion Canyon community falls into the latter category. The high risk zone includes about a dozen homes, garages and outbuildings in the community of less than 300 people.
Lund said the rockfalls of the past paint a risky future for residents — who need to be fully informed of the danger and given the opportunity to stay put or move.
"We were a little concerned our recommendation was too blunt," he said, "but "nobody should go in there and buy one of those houses and be unaware of the hazard."
Last year, nearly 1,400 cubic yards of rock and boulders fell from a steep slope below a cliff and shattered into many fragments. It then moved downslope and killed Maureen Morris and Jeff Elsey.
The rocks — including a boulder that weighed 520 tons — destroyed the house and detached garage.
"Rockville has a long history of large damaging rockfalls," Lund said. Three in recent years have hit occupied homes, and the other two incidents easily could have been fatal. Given the pattern, the scientist said there is a 46 percent probability that there will be a huge rockfall each year.
"When you are dealing with geologic hazards, that is an astronomical figure," he said.
In the aftermath of the latest rockfall, a geologic probe by the survey has revealed that a second, large, joint-controlled rock mass is partially detached from the cliff face above the site and could fall at any time. The slope below the cliff is littered with boulders related to both the Dec. 12 and earlier rockfalls.
The Utah Department of Transportation also conducted an analysis with its geotechnical engineers, concluding that any type of mitigation work such as rockfall fences would be ineffective due to the sheer immensity of what could fall. Their investigation points to two options for impacted residents: move, or remain in place and risk signficant property damage, injury or death.
Rockville Mayor Tracy Dutson said the town wants to make sure the report is available to residents, but he is not sure what options there are for individual households.
"If there are possibilities people want to pursue, we will assist in that," he said.
Rockville is bisected by state Route 9 and is narrowly flanked by the Virgin River to the south and the Rockville Bench to the north.
Dutson said the geographic confines leave little to no options for relocation in the area.
"We're sandwiched between the rock and the river," he said. "That is why Zion Canyon is there, the earth working its magic. There's just not a lot of buildable space up that canyon."
But Lund said it is not unprecedented for Utah cities to relocate people and real property because the risks are too unacceptable. Cedar City and communities along the Wasatch Front have had to purchase properties and "retire" them because of landslides or collapsing soils, he added.
"The entire Zion Canyon is beset by a whole series of different kinds of hazards. It is tough country to live in. There have been any number of communities that have just picked up and moved," Lund said. "Zion Canyon has a history of failed communities and they failed because the hazards were just too intense."
Contributing: Andrew Adams