SALT LAKE CITY - Several boulders as large as a delivery van fell hundreds of feet, destroying a chalet-style house and killing a middle-aged couple in a small Utah town outside Zion National Park, the mayor said.

Rockville Mayor Dan McGuire described a gruesome scene with rescuers finally reaching the bodies of the victims early Friday. He said other nearby houses remain in danger in the town about 250 miles south of Salt Lake City.

The Utah Highway Patrol took geologists to the top of the cliff by helicopter to examine the dangers.

McGuire said the $380,000 house was "totally flattened" Thursday evening. "It was just like an explosion" that left a huge cloud of dust.

The sandstone blocks fell 200 to 300 feet from the top of the cliff, helped by recent freeze-thaw cycles that are continuing, he said.

"They're big slabs of stone with creases and cuts, and they're not all fastened up there," McGuire said. "They have a tendency to push out at this time of the year."

Other nearby residents were staying away from houses built close to the base of the cliff. One renter recently left the neighborhood because of the danger, the mayor said.

The community is "shocked," he said. "Just complete, utter shock not being able to comprehend what happened."

The victims' names haven't been officially released. The mayor said they were a California couple who, according to public records, moved to the area in 2006.

Springdale Police Chief Kurt Wright said snow and ice had been building up on the cliff and between boulders.

"It's been tough to see the people show up and crumble into tears," Wright told KSL-TV. "It's been hard for the whole canyon."

The mayor said that rocks are "always falling" in the town about 5 miles from Zion National Park. "That's what makes Zion canyon."

Tyler Knudson, of the Utah Geological Survey, said that rock falls are often triggered by rain or snow, and the town has had plenty of weather recently.

"The snow melts, gets in joints in the rocks," Knudson told KSL. "When it freezes it expands and can trigger rock falls. It is more common in the winter, fall and spring."