Massive landslide in the Nile Valley (Yakima County) blocks State Route 410 and redirects the flow of the Naches River on October 11, 2009.

  • By Priscilla Long
  • Posted 1/06/2010
  • Essay 9224

On October 11, 2009, at 6 a.m., a massive landslide in the Nile Valley demolishes a half-mile of State Route 410 and redirects the flow of the Naches River. This is one of the largest landslides in the recorded history of Washington. It occurs near the small Yakima County community of Nile located in the eastern foothills of the Cascades about 10 miles northwest of Naches, near Cleman Mountain. State Route 410 travels west from Yakima through the Nile Valley and across the Cascades at Chinook Pass. The landslide lifts this road and breaks it into huge slabs of asphalt scattered every which way. It lifts the river, leaving rainbow trout dying among high rocks that used to be the riverbed.  Five homes are damaged or destroyed in the landslide and another 20 are damaged by flooding as the river finds its new way around rock and debris some 40 feet thick. The slide covers 80 acres, taking several power poles; as a precaution Pacific Power cuts service to about 800 customers. Residents of the sparsely populated area are evacuated. Factors causing the landslide are speculated to be the action of the Naches River undercutting the steep slope, the slippery geological situation of a layer of basalt sliding over a deeper layer of sand, and the activities of a gravel quarry engaged in undercutting the slope.

Cracks and Little Rocks Sliding

Transportation Department crews began monitoring the area on Saturday, October 10, 2009, when the hillside began its ominous dance. On that day residents noticed their land heaving. "We've been listening to it for about two weeks," resident Frank Koch told a reporter, "cracks and little rocks sliding" ("Nile Valley in a State of Upheaval").

Early on Sunday morning, October 11, residents reported popping, grumbling sounds, a "slow-motion mass of grinding rock and dirt" ("Nile Valley in a State of Upheaval"). Steve Smith and his wife, Mary, witnessed the long slow slide destroy their home. Observer Chris Rodriguez described it as "like a knife had cut through the hill and moved everything to the side" ("Slide Blocks SR 410 Near Naches ..."). Throughout Sunday the "heaving mass" continued heaving. The landslide dammed the Naches River, which did not back up but found its way around, causing flooding as it went.

Immediately, the Washington State Department of Transportation (WSDOT) and Washington State Police closed 47 miles of SR 410. At first emergency crews attempted to turn the Nile Road, which ran along the south side of the river parallel to SR 410, into a detour route. But by 10 a.m. the continuing landslide damaged that road and the flooding river submerged it. There was a last-resort exit, a gravel mountain road available for evacuations and emergencies. An ambulance was stationed above the slide and the Nile-Cliffdell firestation west of the slide was available in case of need. Also a helicopter could be employed in an emergency. However, no one was injured in the landslide.

Evacuated were about 60 residents of Nile and 16 boys from the nearby Flying H Ranch, a residential program for troubled boys. Due to the loss of power and the road closure, all guests at the nearby Squaw Rock Resort departed. The resort's store stayed open during the power outage and was thus able to provide supplies to the cut-off community.

Emergency shelters were set up on both sides of the slide, at Nile Valley Community Church and at Naches Valley High School. The Red Cross was on hand.

Emergency Response

After seeing to the safety of people in the area, there were two urgent tasks. One, the responsibility of WSDOT, was to build a passable temporary emergency road. The other, the responsibility of Yakima County, was to rechannel the Naches River, which was in the process of destroying houses and the Nile Road. Of urgent concern was the Nile Road Bridge downriver, and farther toward Yakima, the city's water-treatment plant, situated on the Naches River, which could conceivably have to be shut down due to the inundation of silt from the flooding river. The destruction of either one of these would increase the already high cost and consequences of the disaster by millions of dollars. The other pressing issue was that of insurance or possible federal aid for those who had lost their homes.

On October 13, Governor Chris Gregoire (b. 1947)  proclaimed a state of emergency in Yakima County, which enabled WSDOT to contract for work on an emergency basis. Yakima County commissioners also signed an emergency proclamation to enable the river rechanneling to proceed on an emergency basis. The governor toured the area on October 17. She discussed the state's application for FEMA (Federal Emergency Management Agency) aid. (This was later turned down because the damage was not extensive enough to qualify.)

On October 12, WSDOT work crews began constructing a temporary roadway around the slide to restore emergency services to the Nile Valley and WSDOT re-opened all but four miles of SR 410.  "Things are moving right along," WSDOT spokesman Mike Westbay said, "no pun intended" ("Construction Begins ..."). The Nile Loop Road emergency detour opened on October 20. From October 22 to November 25, WSDOT built a winter-durable detour on SR 410 around the landslide.

In the hectic days immediately following the landslide, Yakima County purchased 60 acres of land, including several homes, to provide room for the new Naches River channel and a new road. The price paid, $1.78 million, was later criticized as being 40 percent more than the assessed value of the properties -- a waste of taxpayers' money. The county defended its  property-acquisition payments on the grounds that immediate action was required to prevent the washout of the Nile Road Bridge and the destruction of the City of Yakima's water-treatment plant.

On November 16, Yakima County began diverting the Naches River into a new river channel to keep it away from the toe of the landslide and to prepare for seasonal flooding. On November 18 through the following day, fisheries biologists from 10 agencies and volunteers worked in shifts to save fish that were stranded in pools of water among shrubs and cottonwoods as the river receded into its new channel. Of particular concern were resident bull trout and steelhead.

The Question of the Quarry

From the beginning there were questions and speculations about the role of the quarry. Simmons and Son Hauling & Rock Crushing had been operating (since 1984) a gravel pit at the site of the landslide.  Rock from this quarry supplied aggregate for road building. Up to the time of the event, the operation had been "digging at the toe of an active slide" ("State Warned Gravel Pit ...") 

What is the toe of a landslide? Imagine dumping a load of gravel down a staircase. The point where the gravel stops, a few feet from the bottom step, is the toe. If you begin shoveling away the toe, more debris will slide down.

In 2005 a geologist from Washington's Department of Natural Resources (DNR) inspected the Simmons quarry and noted a 10-foot gap between the towering basalt cliffs and "a broad talus slope below" ("State Warned Gravel Pit ..."). A talus slope is a broken-rock slope under a steep cliff formed over geologic time from rock and debris fallen from the cliff.

After the 2005 inspection, DNR informed the Simmons firm that, "Your surface mining activity may be exacerbating slope instability and, therefore, may be creating a potential hazard to adjacent property and danger to the public health, safety [and] welfare" ("State Warned Gravel Pit ..."). The department sent a series of letters to the firm insisting that it conduct a thorough analysis and prepare a regular plan for monitoring the slope. As of July 2008, the department had not received a plan. State geologist Dave Norman stated that the agency had been frustrated with the mine owners' lack of compliance. He said "It's been a struggle" ("State Warned Gravel Pit ...").

Conversely, a Yakima geotechnical engineer who conducted a slope analysis for Simmons and Son said that the gravel mine was too small to have triggered the slide. Owner Robin Simmons said an analysis conducted for the firm in 2007 found no reason for concern.

The firm lost a considerable amount of equipment in the landslide and there were Simmons family members who lost homes.

On November 9, 2009, as the firm announced plans to continue mining, the DNR issued an emergency order to suspend mining at the quarry effective immediately.

A Land of Landslides 

In ancient times, Cleman Mountain, immediately north of the present landslide, was considerably rounder. The mountain sloped down to the ancient Naches River Valley. About a million years ago, the folding of the earth and undercutting by the ancestral Naches River (and possibly an earthquake) caused a cataclysmic landslide, known as the Sanford Pasture Landslide. During this event, the south side of Cleman Mountain collapsed and filled the Naches River Valley with a thousand feet of debris. The landscape formed by this prehistoric landslide debris extends from the base of Cleman Mountain for six miles to the east. The formation is known as Sanford Pasture. (The present landslide occurred on the very west end of the Sanford Pasture slide.)

Much later than the Sanford Pasture Landslide, thousands of years ago, the Naches River undercut the edge of the Sanford Pasture formation and another massive landslide occurred. The Naches River was blocked and filled with hundreds of feet of debris.

Over time, debris from this later landslide largely eroded away, leaving a hillside where ultimately homes were built and leaving a talus scarp. (A scarp is a steep cliff left after material breaks away; talus is rock or rubble fallen from a scarp.) The old landslide scarp eroded into an 800-foot-high talus slope. This slope at the west end of Sanford Pasture, where the Simmons mine operated, had been cracking since 2005. On October 11, it was this slope that slid into the Naches River, moving the hill on which the homes were built.

What Next?

By November 25, in time for Thanksgiving, WSDOT opened the rebuilt SR 410 to traffic. The finishing touches such as guardrails and guideposts were completed in early December. Businesses that suffered economic losses due to the slide were able to seek low-interest disaster loans from the federal Small Business Administration, which set up customer-service representatives nearby in mid-November.

In early December Washington's Department of Ecology announced a $240,000 grant to Yakima County to offset the costs of redirecting the river.

A concern is that the Nile Valley landslide will trigger an even larger landslide in this area of historic landslides. WSDOT has installed radar to continuously scan the slide area and provide early warning if the larger slope becomes unstable. Another surveillance tool in use is a long-range laser surveying system called LIDAR. This instrument provides detailed topographical snapshots to detect movement as tiny as three inches. Seismometers installed by University of Washington scientists are also monitoring the area.

Sources: Melissa Sanchez and David Lester, "Massive Landslide Shuts Highway, Clogs Naches River," Yakima Herald-Republic, October 11, 2009 (; Melissa Sanchez, "Construction Begins on Detour to Replace Buried Section of SR 410," Ibid., October 13, 2009; Melissa Sanchez and Phil Ferolito, "Nile Valley in a State of Upheaval," Ibid., October 13, 2009; David Lester, "Landslides are Nothing New in Nile Valley," Ibid., October 13, 2009;  Lester, "Businesses Affected by Slide Can Seek Low-Interest Loans," Ibid., November 13, 2009; Lester, "Yakima County Defends High Cost of Buying Nile Property," Ibid., November 21, 2009; Lester, "$240,000 State Grant Heading to County for Nile Slide Costs," Ibid., December 7, 2009; Sandi Doughton, "Gravel Quarry Near Landslide Ordered to Halt Mining," The Seattle Times, November 6, 2009; Doughton, "State Warned Gravel Pit of Slope Instability 4 Years Before Landslide," The Seattle Times, October 16, 2009; "Slide Blocks SR 410 Near Naches, Forces Evacuation," The Seattle Times, October 11, 2009; "Take a Trip Up SR 410 -- It's Open," Yakima Herald-Republic, December 28, 2009; "DNR issues Emergency Order to mine operator at the Nile Landslide near Naches," News Release, Department of Natural Resources, November 5, 2009 (; Washington Department of Natural Resources, Emergency Order to Suspend Surface Mining, November 4, 2009 (; Sliding Thought Blog (; Shannon Dinney, "Biologists Work to Save Fish After Landslide," The Spokesman-Review, November 21, 2009;  "SR 410 Nile Valley Landslide," Washington State Department of Transportation (WSDOT) website accessed January 4, 2010 (; "Gov. Gregoire proclaims emergency in Yakima County due to State Route 410 damage," News Release, October 13, 2009, Governor Gregoire's website accessed on January 6, 2010 (; Meagan McFadden, WSDOT Communications, Yakima, email to Priscilla Long,, January 7, 2010, in possession of, Seattle.

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