Adam Spencer, The Triplicate

High cost to go around troubled stretch of highway

In 1972, Kurt Stremberg's parents dropped him off in Klamath and said goodbye before he headed on a post-college-graduation trip to Europe. Stremberg had no idea that it would be the last time he ever saw them.

During his parents' drive back to Crescent City, part of the incredibly unstable section of U.S. Highway 101 known as Last Chance Grade collapsed, tumbling into the Pacific Ocean and taking Stremberg's parents with it.

"That road is going to go again - it's just a matter of time," said Stremberg, a longtime local real estate agent, on Wednesday during a meeting of the Del Norte Local Transportation Commission.

The commission was receiving an update from Caltrans officials for ongoing and planned construction at Last Chance Grade, which is scheduled to open for two-way traffic by the end of October - the first time in almost a year.

More than $29 million has been spent stabilizing and repairing Last Chance Grade, which begins 12 miles south of Crescent City, where highway views abruptly switch from old-growth redwoods to soaring views of the Pacific.

In recent months, multiple local agencies, including Crescent City Council, Crescent City Harbor and the local Chamber of Commerce, have sent letters voicing their support for re-routing 101 around the Last Chance slide, but the price tag is staggering.

Talitha Hodgson, Caltrans project manager for Last Chance Grade, said that similar bypasses she has researched cost $60 to $70 million per mile, and one studied bypass for Last Chance was at least four miles long.

The 2002 Caltrans report on alternatives that included the four-mile bypass through timber land and state park property east of Last Chance Grade said that it would impact three acres of old-growth redwoods. Hodgson made sure to note that the bypass projects she used for comparison did not involve old-growth redwoods, park land, or the constraints of building in a coastal zone.

Future plans for Last Chance

Caltrans is hedging its efforts to protect the slide-prone section of highway with an engineered feasibility study, with an expected completion date of June 2015, that will analyze several previous studies and any other information available to develop and explore alternatives to continuously repairing and rebuilding on the current alignment.

This month marks the completion of a 180-foot long and 40-foot high retaining wall that was built for $4.8 million to protect an existing wall that was built in 2010 but had partially failed from the strong forces of slides.

Pending any unforeseen slides or extensive damage, Last Chance is expected to remain a two-lane highway until summer 2016, when another multi-million dollar project to construct a soil nail wall will start.

Members of the Del Norte Local Transportation Commission vocally worried that the entire section of highway could fall into the ocean before that. The commission is hoping Caltrans will complete an economic impact study for Del Norte County of a Highway 101 closure.

Sharon Frymer, vice president of the Klamath Chamber of Commerce and owner of Woodland Villa restaurant and store, called the integrity of Last Chance "deplorable" and said that if the road failed entirely "Klamath would cease to exist."

If 101 at Last Chance Grade were to fail, it would take 5andfrac12; hours to drive about 200 miles between the two areas - and that's just during dry months.

In the winter, when the short-cut, seasonal Grayback Road from O'Brien, Ore., to Happy Camp is closed for snow, it would be an eight-hour drive of 300 circuitous miles to get from Crescent City to Klamath, whether that be for work, school, medical services, police response - anything.

At least 100 students in Klamath attend schools in the county north of the slide on Last Chance Grade.

How unstable is it?

The ground at Last Chance grade moved horizontally four to 13 inches from July 2012 to February 2013 and dropped vertically three to ten inches. Even during the dry season (from February 2013 to September 2013) the ground moved horizontally two to four inches and dropped vertically one to three inches, according to Caltrans.

Hodgson said the culprit is deep-seated landslides, shallow flows and many other geological forces at work.

Bob Busch, a certified engineering geologist who has worked in the area for more than 30 years and owns Busch Geotechnical Consultants, has conducted two substantial studies on Last Chance Grade, one in 2012 and one in the late 1980s.

Busch's team examined many paired aerial photos of the area dating back to the 1940s and identified a similar pattern:

Once trees on the slopes below the road reached a certain size, the entire hillside holding them up would give way.

"The weight of trees on the soil would be too much and after some great rainstorm the entire area would slide down into the sea," Busch said.

This type of episodic land sliding is called a debris slide, and Last Chance is on a debris slide slope. The large landslides happen all at once, instantaneously breaking loose and heading toward the ocean, Busch said.

Busch said that the fact that one of Caltrans' "beautiful" retaining walls failed indicates that a debris slide already tried to happen.

"What it means is that there is an enormous mass of rock that's trying to slide down and pull off the face, taking the road with it, Busch said, adding that is why Caltrans probably started stabilization work on the downhill side of the road as well.

Once Highway 101 opens up to four-lane traffic, still north of Wilson Creek, there is another geologic force at work: earthflow.

Unlike the catastrophic rapid failures of debris slides, earthflows are more like a very slow-moving, bumpy conveyor belt, always moving towards the ocean, Busch said. This frequently creates cracks in the highway.

But the real question, Busch said, is that with scientists predicting a massive Cascadia subduction zone earthquake in the near future, could whatever Caltrans builds withstand the disaster?

"Pretty much all of us geologists think that there's not a snowball's chance in hell that a lot of things won't go down on the coast," Busch said. "I predict that during the Cascadia quake, that some section of Last Chance Grade will be one of the likely places to go."

Reach Adam Spencer