Ten families who lost relatives in the Oso landslide in March have sued Snohomish County, the state and a forest landowner, alleging that the disaster was not natural but the result of a series of “actions and inactions” by those parties.

The lawsuit was filed Friday in King County Superior Court and seeks an unspecified amount of damages.

The March 22 landslide in Snohomish County was caused by a massive slope failure that pushed across the North Fork of the Stillaguamish River into the Steelhead Haven development, killing 43 people.

This lawsuit was brought on behalf of 10 families and their 14 deceased relatives. State law allows the filing of such lawsuits in an adjacent county, said Corrie Yackulic, the Seattle attorney who filed the lawsuit.

The lawsuit filed Friday is part of a broader wave of litigation expected in the aftermath of the tragedy.

A separate lawsuit filed in King County Superior Court in July and since amended seeks damages on behalf of the families of nine other Oso slide victims, naming Snohomish County and the Washington Department of Natural Resources as defendants.

The Seattle Times reported in March that since the 1950s, geological reports on the landslide zone included pessimistic analyses and the occasional dire prediction of future slope failures, and that the state used outdated boundaries to restrict logging above the slope that collapsed.

The recent lawsuit filed by Yackulic alleges that landside risks were well understood by local and state government, as well as Grandy Lake Forest Associates, which owned a 7.5-acre parcel that was logged in 2004 above the slope.

But important information about these risks was never shared with homeowners, the lawsuit alleges.

The lawsuit cites the comments of Gerald Thorsen, a state Department of Natural Resources geologist who visited the landslide zone two years after a 1967 slide. He cautioned that “this slide has shown that major construction below any of the old scarps should be done with extreme caution.”

Yet the state and county did not take “extreme caution” in allowing development below the slide area, the lawsuit alleges.

The lawsuit also contends that the county led Steelhead Haven residents to believe that risks had been addressed by installation of a log crib wall at the base of the Hazel Landslide. The court, according to the suit, did very little to inform the residents of Steelhead Haven of the “life-threatening dangers they and their families faced living in the potential run-out zone.”

Snohomish County chief civil deputy Jason Cummings said Monday he was unaware if the county had been served the complaint and declined further comment.

“At this time, our thoughts are with the families who lost love ones,” Cummings said.

Ken Osborn, manager of Grandy Lake Forest Associates, said Monday, “I think we did things by the book and our hearts go out to the victims.”

A spokeswoman for the Department of Natural Resources, which approved the 2004 logging, could not be reached for comment.

Hal Bernton: 206-464-2581 or hbernton@seattletimes.com

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