Workers secured by ropes strained against crowbars to dislodge massive boulders perched above Interstate 5 at the Siskiyou Summit Wednesday.

Workers secured by ropes strained against crowbars to dislodge massive boulders perched above Interstate 5 at the Siskiyou Summit Wednesday.

When that didn't work, they tried cables rigged to a backhoe. But the cables snapped trying to pull down 40 tons of rock and dirt 60 feet above the ground.

After all the cables broke and a little of the rock rained down, the Oregon Department of Transportation briefly thought of another option — dynamite — but decided it would be too dangerous and settled on bringing in stouter cables today.

In the past six weeks, boulders have been tumbling off a steep cliff on the west side of Interstate 5 at the summit. A boulder the size of a car came down in October. ODOT decided to shake loose some of the worst spots before more rocks fall down in heavy snow or rain.

ODOT geologist Kim Wyttenberg said that if even a small boulder tumbled onto the interstate, it would cause serious problems.

"It would squish a semi," he said.

Rock scalers from PKO Consulting of Roseburg and ODOT crews managed to knock down about 10 yards of material Wednesday, enough to fill one large dump truck. ODOT officials estimate there is another 60 yards of loose material left on the rocky cliff, cut when the freeway was built in the 1960s. The contract for the work with PKO is $5,000.

Crews used a 5/8-inch cable because it was easier to hoist up the 60-foot rock face, but plan to use a 3/4-inch cable today. The rock scalers attached the cabling on the cliff while an ODOT backhoe below pulled.

ODOT slowed traffic to less than 20 mph on the freeway to create windows of time for the workers to do their job without shutting the interstate down.

Wyttenberg said dynamite is an option, but it has other problems.

"Blasting is more dangerous," he said. "We would have to stop the whole freeway."

The explosion could jar other parts of the crumbling cliff loose that could later fall onto the road, he said. Blasting also is more expensive, he said.

The cliffs on both sides of the freeway are made up of layers of volcanic flows which used to be an ancient sea floor millions of years ago.

Layers of loose fractured rock sit under more solid formations. When the loose rock sloughs off, the heavier boulders eventually begin to fall.

Wyttenberg pointed to old tree trunks fossilized in the rock formations. He said they were a darker color because they were originally charred wood.

He said the cut for the freeway is in a mountain that is leaning to the east. Wyttenberg explained that most of the dangerous debris falling down is coming from the west side of the freeway because it tends to lean to the east.

As a backhoe chugged back and forth attempting to break a boulder free, ODOT District Manager Jerry Marmon said the chunk of mountain was actually moving about 6 inches or more. But the heavy rock was still pinned, preventing it from fully breaking free.

While crews tried to dislodge the boulders, traffic was temporarily prevented from coming over the pass because of the danger that a rock could roll onto the freeway, said Marmon.

The operation is taking care of boulders and other overhanging rock formations, but the steep, fractured cliff will still not be perfect.

"We're trying to address the worst of the worst," said Marmon.

ODOT hopes the operation will make the summit safer during the winter.

"In the worst-case scenario these rocks would come down in the middle of a snowstorm," said Marmon.

Reach reporter Damian Mann at 776-4476 or dmann@mailtribune.com.