SALT LAKE CITY – More cliff-top rocks similar to ones that killed a middle-aged couple when they smashed into their home near Zion National Park could come loose, Utah geologists warn.
A 375-foot high sandstone slab near the former rock slide now threatens to crash, shatter and flatten homes below, according to the Utah Geological Survey report released Thursday.
When it comes to hazards of falling rock, "some are annoyances, some are deadly," said Bill Lund, a senior scientist at the Utah Geological Survey. "And we're dealing with one of the deadly ones here."
There's "no question," said the report, that future rock falls will hit Rockville, population 250. The report comes from a team of state geologists who surveyed the December wreckage and nearby cliffs on foot and from a helicopter.
Rockville Mayor Tracy Dutson declined an interview but said in an email that the town would use the report to help current residents and potential homeowners there understand the risks.
The warning comes less than two weeks after at least 30 people were killed by a mudslide in Washington state.
In mid-December, officials recounted, an explosive boom sent up a cloud of dust just before dinnertime on a Thursday evening, killing the couple and crushing their small chalet, garage and the front half of a Hyundai SUV.
Other looming rock masses and crags could unhinge at any moment, Lund said, tumbling down onto a string of homes in and around Rockville, about 250 miles south of Salt Lake City.
Residents should pack and move, they caution, or understand that they could die if they choose to stay.
Rockville faces higher risk than neighboring Springdale and La Verkin because the canyon walls taper in there, forcing homes to huddle closer to cliffs.
"They just don't have a lot of room to maneuver in that town," Lund said.
The massive December slab shattered when it hit an underlying slope a bit steeper than a typical mall escalator and sent boulders racing down onto the Main Street home, the report found.
The largest boulder to slam the home weighed 520 tons, nearly as much as over 30 gravel-filled dump trucks.
It marked first time anyone in Rockville has died, but the sixth time hulking rock has fallen in the last 13 years and the third to strike a building, the report finds. Since 1850, Utah has counted at least 20 deaths from falling rock.
An earlier report from the same team of geologists in 2011 pointed out hazardous areas, which included the home destroyed in December.
Efforts to brace against the falling blocks, including fences, or bolts into cliffs likely won't prevent future slides, it found.
The report recommends the town try to buy up homes and lots in dangerous areas but says it's unknown if federal, state or other sources could help relocate residents.
Joe Dougherty, spokesman for state Division of Emergency Management, said he didn't know if the division would help residents move. About a decade ago, he added, the division helped secure a federal grant to buy homes in a North Salt Lake community plagued by mudslides.
Rockville, with neither a stop light nor a schoolhouse, lies five miles west of Zion National Park, known for its soaring red rock and emerald pools.
The half-mile town's 250 residents include year-round residents, as well as those who own vacation homes, said Elaine Harris, the town clerk.
Maureen Edgel, owner of the Desert Thistle Bed and Breakfast in Rockville, said the December deaths saddened the close-knit town and jostled nerves there.
"When you see the house demolished now and it's just big rocks," she said, "it's sad to know that you know someone one day and the next day they're gone."
But Edgel noted, most residents understand the threat: Boulders every so often tumble into southern Utah swimming pools and backyards.
"I don't think we really fear it," she said. "I think most of us just go on about our daily work."