As dramatic as it appears, a large crack along Rattlesnake Hill — the ridge separating Union Gap from the Lower Valley — isn't expected to cause disaster anytime soon, experts say.
So far, the slow-moving landslide hasn’t presented as much of a threat as a rock slide near the Nile in 2009, which buried a half-mile stretch of State Route 410 near Nile and rerouted the Naches River.
It's a reminder of another rock slide that occurred in the 1980s along Yakima Ridge, which divides Yakima and Selah.
Though varying in magnitude, all three disturbances have one thing in common — adjacent gravel mining operations.
There’s nothing definitive saying mining operations caused those slides, experts say.
Those aren’t the only concerns surrounding mining operations. Neighbors often complain about increasing dust, noise and truck traffic when operators seek mining expansion.
But one thing is certain: there’s a real need for aggregate in Yakima County.
Demand for aggregate
The Washington State Department of Transportation officials say there’s an estimated $40 million in road construction and maintenance projects this year alone in Yakima County.
Half of the projects consist of repaving roads with the rest being bridge and deck rehabilitation, said Troy Suing, DOT’s regional administrator for planning and program management. Work will be done on three bridges this year in North Yakima on U.S. Highway 12, Interstate 82 and the North First Street ramp, Suing said.
All work here is done by private contractors and the state and county typically go with the lowest bid.
Having local material helps keeps cost down by reducing transportation expenses, he said.
Yakima County Planning Official Tommy Carroll said years ago the county identified all areas suitable for mineral resource overlays, a designation that allows property owners to seek a mining permit and begin gravel mining operations.
Operators have to provide the county with a full site plan, including locations of the mining pit, stock piles and the office.
Often times mines are cut into ridges because that’s where the best aggregate is at, Carroll said.
But you do take a chance when you mine into the side of a ridge, he said.
“It’s hard sometimes to determine integrity of a ridge,” he said. “We have no mechanism to drill into the side of it to determine geology.”
The crack on Rattlesnake Hill was discovered in October 2017 and an investigation was launched.
Columbia Asphalt and Gravel, which operates a gravel mine near the base of the crack, moved operations to the east, away from the areas of concern.
It’s not clear whether mining caused the crack.
Steve Reidel, a former adjunct geology professor at Washington State University’s Tri-Cities campus, doesn’t think so.
He said the crack emerged from one of several old faults formed millions of years ago. He said water gets into areas where the rock is weak and over time it starts to slide.
However, there hasn’t been much recent movement there, he said.
“I don’t think it’s ever going to be anything worse that it is,” he said. “Last time I looked, it was just barely moving. We have a joke over here that it’s a constipated landslide.”
Reidel said it looks like the slide is actually moving into the gravel mine rather than down the western slope where Interstate 82 and the Yakima River are below.
“It looks like everything is just stopping at the quarry, it all seems to be backing up there,” he said.
“It looks like the quarry is stopping the main movement. This is why we call it a constipated slide.”
Information of this “slow moving slide” can be found on the state Department of Natural Resources website.
Rattlesnake Hill is far less dramatic than the one that occurred on State Route 410 near Nile on Oct. 11, 2009.
That slide buried a half-mile stretch of 410, and rerouted the Naches River.
Some thought the slide may have been related to mining at a nearby rock quarry, said Newell Campbell, who once taught geology at Yakima Valley Community College.
“It was a small operation and it was a huge slide,” Campbell said. “I don’t think it was that much of a factor.”
The recollection sparked Campbell’s memory of another much smaller slide that occurred on Yakima Ridge in the 1980s.
That slide, which may have been caused by mining or a road installation, was about 100 yards across halfway up the ridge’s south side and blocked an irrigation ditch, Campbell said.
“They got in there and fixed that,” he said.
Push comes to shove
Granite Northwest Construction mines the Yakima Ridge, but operations there are on hold as the company has entered settlement talks with the Yakama Nation. The tribe sued the mining company, saying the entire ridge is a cultural site that should be protected.
Granite is now getting aggregate from DTG’s mine on Rocky Top in west Yakima.
The company has an operation agreement with DTG and the area is properly permitted, Planning Official Carroll said.
“They’re following the permit and everything,” Carroll said.
But Columbia Asphalt hasn’t been as fortunate. The company is working with DNR and has decided to cease operations at Rattlesnake Ridge, and doesn’t anticipate mining the site anytime soon, said company spokesman K.C. Klosterman.
“Whether that's 10 years, or 20 years or 30 years, we’re totally going to put that in the hands of the Department of Natural Resources and that will determine whether the site is ever mined again,” he said.
Klosterman said the company is looking for other areas to mine, most likely on flat ground rather than ridges, to meet demand for material.
“We need those aggregates for road maintenance and road development preservation, and we will be eventually bringing other aggregate resource sites to the market, but likely they'll be sand and gravel instead of quarried stone,” he said.
Common sense dictates that aggregate mining should not be located on a hillside next to a freeway, or a river.
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