Oso Strong: Scene of the Slide


On Monday morning, March 22, 2014, a woman driving west on state highway 530 to work in Arlington saw something bright in her right window. Then the forest toppled as a monstrous wave slammed into her car, crushing it and her in it.  That was the Oso landslide, the most lethal in American history, killing 43.

Some 25,000 years before, an ice lobe 100 miles wide and three miles thick advanced south from Canada’s Cordilleran Ice sheet into the Puget lowland, shearing off mountain abutments that it crushed and ground into boulders, cobbles, gravel, sand, and finally a meek clay that settled in a sequence of layers at the bottom of meltwater lakes extending eastward into mountain valleys.  The process reversed itself 12,500 years ago when the ice retreated. 

Once the ice reached the Strait of Juan de Fuca, the recessional lakes disappeared into the Pacific, revealing the shocking new landscape of the Puget lowland.   Freed of ice and lakes, mountain rivers cut into the yielding strata.  

The North Fork of the Stillaguamish River heads in in the Cascade Mountains and flows south to the lumber town of Darrington, a narrow portage away from the north-flowing Sauk River.  There the Stillaguamish turns west passing through the little communities of Hazel, Rowan, and Oso. It meets its South Fork at Arlington on its way to Puget Sound.  As the meandering river eroded the base of its steep valley walls, the lofty lake sediments tumbled.  

Native Americans who watched all this settled in winter villages at Sauk Prairie, east of Darrington, and in the flatlands west of Arlington.  The North Fork’s unstable valley proved too dangerous for anything more than temporary fishing camps.  

When American settlers moved up-river in the 1880s, mining and lumber camps became small towns.  In 1901, the Northern Pacific Railroad built a spur to Darrington and logging soon denuded the valley slopes.  Especially dangerous was the valley’s narrowest part near Oso.  Six miles east, a part of Whitman Bench, the lake deposits of the north valley wall, slid in 1937.  In 1949 a much larger slide there engulfed a half-mile of riverbank.  Timber cutting nonetheless continued.  Drawing from several reports Priscilla Long and other historians documented subsequent events.  

In 1951, another section of the same area collapsed, sending debris once more to the riverbank.  In 1960, ignoring local names like “Slide Hill,” and “Mudflow Creek,” a developer platted a recreational community called Steelhead Haven on the south bank directly across from the unstable slope.   Lots zoned for single family residences neatly avoiding a permitting process that would have warned of dangers.   

In 1967 the slope failed again, flooding 48 lots and damaging or destroying 25 cabins.  The State Department of Natural Resources warned that any construction in the area should be done with “extreme caution.”  Building continued regardless, and in 1999 the U. S. Army Corps of Engineers warned about “large catastrophic failure” of the slope.  A firm hired by the Stillaguamish tribe that fished the river there pointed out that “catastrophic-failure potential places human lives and properties at risk.”

In 2005, the Tribe obtained funds to move the river channel 430 feet south of the weakened slope, but a year later another great slide pushed the river 730 feet south free of charge.  A 1,400-foot log and concrete revetment designed to confine silt did not stop the river from undercutting the north bank, further weakening the slope.  No one had been killed in Steelhead Haven, but in accordance with federal law, Snohomish County commissioned in 2010 a report that described the hillside along the North Fork as one of the “most dangerous.”  

The 2006 slide left hummocky terrain that captured precipitation.  Water percolating through gravel and sand to impermeable clay added unsupportable weight to the overburden.  The winter of 2013/14 had been dry, but March witnessed heavy rains, and on March 23, at 10:37 am, “Slide Hill” gave way.  

With movement, internal cohesion vanished; the deposit liquified, reaching speeds of 40 miles per hour as it hydroplaned across the river into Steelhead Haven.  A survivor recalled the sound of “10,000 things hitting each other.”  Another part of the hillside gave way adding momentum.  In its few minutes’ surge, 19 million tons of debris buried a half-square mile to depths of 70 feet.  A total of 49 homes were destroyed, a half-mile of Highway 530 was covered, and the North Fork dammed.  After the mighty slide stopped the only sounds piercing the awful silence were screams.

This last October smoky haze veiled the mountainsides.  The impounded river flowed freely, and the road was clear. In the intervening years, new growth has covered much of the debris field.  The baleful hillside scarp still gleams fresh in the distance as it did for that driver a split-second before her death eight years ago.  

At the memorial, a long iron gate bars passage to the unconsolidated rubble. Signs hanging from it offer solace: “We Are Family,” Oso Strong,” “Always In Our Hearts, Never Forgotten,” and a reflection: “Grief is the price you pay for love.”

Footsteps beyond, unsteady gray hummocks of sandy clay are strewn with shattered logs, plastic fencing, and a broken coffee mug.  A thickening snarl of resurgent vegetation resists access. Horsetails, woodfern, coarse grasses, loosestrife, scrubby willow, cottonwood, and a nightmare of Himalaya blackberry vines–rugged first responders to natural catastrophe.  Here and there rises a sapling fir or cedar seeded by obliterated sires. 

Near the highway stands a row of bronze, assorted mailboxes numbered but welded shut: delivery no longer possible.  There are 43 cedars in several rows representing the victims. Family members have decorated the cedars with roadside memorabilia: painted hearts, rocks, shells, beads, plastic flowers, mugs, photos, children’s drawings, citations of veteran status, high school teams and a full bottle of Bud Lite.  Beer cans hang from branches—“Grandma’s favorite,” with toys and ubiquitous teddy bears. 

Plans call for expansion.  But this viewer is left pondering what the Memorial asks us to recall.  Surely the victims ranging in age from four months to 91 years and their community: the 900 who rushed to save survivors and labored months to retrieve the dead.  But I also wonder what inclined families to live with their children at a site long known to be dangerous?  Who permitted it?  

The state allowed the clear-cutting.  County officials kept issuing building permits at Steelhead Haven.  A week after the slide, a spokesman for the Snohomish County Department of Emergency Management said, “…the hillside that collapsed had been considered ‘very safe’ and the slide came out of nowhere.”   However, lawyers have since won judgments approaching $100 million.

In 2015, the Washington Legislature mandated that the State Department of Natural Resources begin collecting information about the state’s geology using the latest technology, especially Lidar (from Light and Radar), in which laser beams map the earth’s surface with often alarming detail.  Lidar sweeps of the North Fork of the Stillaguamish Valley showed the area east of Oso to be literally covered with landslide deposits on both sides of the river, with the edges of the Whitman Bench entirely scalloped by scores of slide scarps.  Statewide, the results promise a revolution in land management—in the future.

If you visit the Oso Memorial, note the broad peak slightly northeast of it.  On its steep, river-facing slope spreads a large clear-cut.  Water percolates to the glacial lake deposits below, unsteady to begin with.  Shock comes with the realization that one stands directly in its path.   

If you like your terror neat, consider that this is the case along the entire valley, on both sides.  In valley after valley after valley.


  1. David,
    Thank you for the helpful and accurate assessment of the landslide danger at Steelhead Haven. Very sad for the many unsuspecting people who lived there. They likely did not know of or understand the dangers that had been mapped by geologists. On a statewide level, one can see that one reason such developments happen is our state legal tradition of honoring “pre-existing” lots, parcels created before our land use laws enacted prohibitions against such things. Washington state has hundreds of such “recreational riverside” lots platted without regard to landslide safety or flood hazards. Hundreds of small lot developments with names like “River Bend” or “Oxbow Acres”. Many with unstable slopes across the river. New homes get built in these places because of the seduction of peaceful river front living. These parcels are “preexisting” the new laws that prevent development in such areas. I have personally attended on site meetings with people building such homes where they are told of the danger, they prefer taking the risk for the beauty of the location, even sign a document that holds the county harmless. Later when a flood or landslide destroys their home, there are natural complaints about “why government” allowed the home to be built”. Denying construction on such a lot brings lawsuits from the so called property rights and libertarian legal aid groups looking for opportunities to “save the little guy from government oppression”. They disappear during disaster time.


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