On May 24, a roadside attraction was created in seconds after two massive boulders tumbled 1,000 feet onto Colorado Highway 145, obliterating a section of highway northeast of Dolores.

One boulder, which weighed 2.3 million pounds, crashed intact onto the roadway, cratering and buckling the road like an earthquake. It was blasted apart for removal.

The other boulder, a 8.5 million-pound chunk of Dakota sandstone, plowed a 15-foot-wide trench through the asphalt and came to rest on the shoulder, where it remains.

A witness said the rockfall sounded like a jet engine, darkened the neighborhood in a cloud of dust and nearly hit three vehicles. Nobody was injured, but a truck was dented by rocks that fell along with the boulders.

Nine weeks later, the highway has been repaired, at a cost of $1.12 million, said Lisa Schwantes, communications manager for the Colorado Department of Transportation Region 5.

“The engineering of the rebuild is impressive, the construction crews did a great job,” she said.

The highway was rebuilt and widened and did not have to be realigned. Project details included:

Widening the road surface by 4 feet to allow for additional shoulder space.Installing a guardrail on the east side of the highway to ensure the safety of vehicles that pass the boulder, which remains on the side of the road.Building an embankment on the western, slope side of the highway to stop any future potential slide from reaching the highway. The embankment bench is 40 feet wide and parallels the highway for 150 feet. It is angled back into the slope and armored with riprap. The bench has channels on each side to route waters parallel to the highway.Relocating a utility fiber optic line.Rubble from the exploded boulder also was used as riprap and for erosion control on the slide scar.

The boulder sparked widespread interest across the state and was named Memorial Rock by Colorado Gov. Jared Polis because it fell over the Memorial Day weekend.

However, the boulder sits on private land, and CDOT and the Colorado State Patrol do not want sightseers to stop along the highway because of concerns about traffic safety and trespassing, Schwantes said.

“No Stopping,” “No Parking,” and “No Standing” signs are expected to be posted along the stretch in the next month.

“We want to deter people from stopping,” Schwantes said. “It has been a novelty, but as time goes on, curiosity will lessen.”

The power of the rockfall and the fact that no one was injured is impressive.

The boulders tumbled between vehicles. Two cars narrowly passed the falling boulder, and a truck driver braked hard and was pummeled by large rocks as he drove in reverse to avoid the falling boulder.

The highway was closed as residents and highway officials looked in amazement at the boulders and their destructive path. One gravel lane was built within three days with a traffic light signal that allowed alternating traffic to pass by.

At times, locals and tourists clogged the construction area and slowed traffic as they took photos. CDOT had the extra task of herding people through the one-lane area.

A geotechnical team surveyed the cliff band at the top of the valley where the rock fall originated, and no immediate signs of pending failure were discovered. Additional surveys are pending.

Contractor GeoStabilization International, of Denver, performed rock blasting and downsizing and removed additional loose rock and debris from the slope. Williams Construction, of Norwood, was hired to rebuild the highway.

A Google Earth image of the section of rock before it fell shows a gap where it was separated from the main cliff band.

The section of cliff wore over time from a combination of weathering, erosion, freeze-thaw cycles, excessive moisture, gravity and perhaps even a 4.5 magnitude earthquake that occurred 35 miles north of Dove Creek on March 4 and reportedly was felt in Cortez.

Expanding ice in a gap behind the boulder also might have contributed to the rockfall, officials said. The phenomenon, called ice-jacking, occurs when water enters a confined space, then freezes and expands, causing structural fractures. Frequent rainfall preceded the rockfall.

Ray Seeley and Dawn Whaley, both of Clifton, were driving southbound when they were struck by falling rocks.

“We came around the curve and saw dirt and rocks flowing across the highway,” Whaley said. “My boyfriend slammed on the brakes, and we were hit by debris. He threw it into reverse, and we backed up 20 feet until blocked by a downed power line behind us.”

When the dust settled, they had stayed on the road and were about 20 feet from a house-size boulder that landed in the middle of the road.

“It was the scariest thing I’ve ever seen. When I saw the size of the boulder, my knees went weak,” Whaley said. “We were very fortunate. Our guardian angels were watching over us.”

jmimiaga @the-journal.com