Big Fill Slide Frequently Asked Questions

Why did the slide occur?
Wyoming State Highway 22, Teton Pass, was constructed to link communities over a mountain range. Whenever you build a roadway through mountainous terrain, there is an inherent risk of mudslides, rock fall, landslides and other earth movement and erosion. With recent rapid warming temperatures (+25 degrees), the snowpack in the mountains melted quickly, saturating the native material under the fill of the road and lubricating the clay materials until it moved. The native soil under the road fill material failed, resulting in it sliding out and causing the road and big fill material to collapse.  

Didn’t WYDOT know the road was failing as soon as the first crack appeared?
On Thursday, when crews responded to the report of a crack in the road, WYDOT geologists were notified, and careful evaluation and investigation of the entire area began. Teton Pass is a young mountain range and has seen geologic movement (in the form of erosion) over time. WYDOT Geologists have been monitoring areas on the pass for many years. An inclinometer previously was installed in the area of the big fill slide to record subsurface movement. It was read on May 15 of this year, and geologists had not seen any unmanageable movement (less than 0.1 of an inch per year) up to that point. 

Unfortunately, Mother Nature and her warming temperatures accelerated the movement. Conveniently, the road was already closed due to a mudslide event nearby on Friday, but WYDOT would have immediately closed the road due to unsafe conditions after seeing the additional movement. Traffic would not have been on the road during the slide if the mudslide had not occurred. 

Why build a road where landslides could occur?
Basically, anytime you build a road through a mountain range, you run the risk of potential landslides. Departments of Transportation across the country work hard to mitigate the risk of road failure. If transportation officials only built roadways in landslide free areas, it would be hard to connect communities throughout the Rocky Mountain Region, or any mountain range. Without these roads, communities would be isolated without access to economic resources and emergency services. 

Aren’t you worried it could happen again?
As with all mountain roads, there is a risk of geologic movement that could affect the road. However, WYDOT is carefully evaluating and working to mitigate risk of road failure. This includes constant monitoring and drilling/sampling investigations, as well as pursuing and completing projects to address drainage improvements and better road design to improve weight distribution to discourage ground movement. The fill material did not fail but went for the ride when the underlying soils reached a point of saturation. The fill is good material and is being combined with quality borrowed material to complete the detour. The natural ground that yielded under the "Big Fill" has a different composition than under the detour. Natural ground below the "temporary" detour is less wet, harder or more compact, and has not been subjected to large "big fill" loads (stress) when compared to the original alignment.

How is the work happening so fast? Doesn’t it take WYDOT longer to get projects constructed?
WYDOT does have an emergency repair protocol in place to address situations like a landslide. Emergencies happen all across the state, and WYDOT is prepared with a team of experts to act quickly when necessary. Responding to these types of emergencies, which includes things like landslides, debris flows/mudslides, flooding and other road damage caused by acts of nature, takes time and money, so it’s not something the agency does for every project. 

As another example, WYDOT would conduct an emergency project to repair a bridge damaged in a crash. 

Why not just build a bridge there?
WYDOT engineers are currently reviewing what kind of permanent design would be the best to build in the area. However, the steep grades would make it difficult to build any kind of acceptable grade with a bridge. This is why you generally see switchback-type designs through the mountains. It’s a safer way to traverse steep grades for vehicles. General safety design indicates that a 5-6 percent grade is a safe steepness for most vehicles. Teton Pass was built in the 1960s with a 10 percent grade. A bridge through the area would more than likely have a 20-25 percent grade. To put it in perspective, average ski hill runs with a “blue square designation” would likely have around a 25 percent grade. It wouldn’t be safe to put vehicles on that steep of a grade in the wintertime on snow packed roads. 

Can WYDOT add a wildlife crossing, bike path or other improvements while conducting these road repairs?
Thanks to the Governor’s Emergency Declaration on June 8, WYDOT is looking to tap into emergency Federal funding through the Federal Highway Administration and the US Department of Transportation. Part of the stipulations of that funding is that the infrastructure has to be rebuilt to its former state. Of course, it must meet today’s construction standards and specifications, but additional infrastructure cannot be added unless paid for with separate funds. 

How is WYDOT going to make sure the temporary detour is safe for travel?
WYDOT is doing a few things to make sure vehicles can safely utilize the detour through the slide area. Crews are addressing drainage concerns to ensure a more solid foundation for the road. Geologists are also mapping the site to confirm there are better native soils under the roadway. In addition, the detour road will put less weight on the active area, relieving some of the driving forces pushing on the slide zone. 

If the detour is safe to travel, why not just build the new permanent road there?
The detour will be steeper with a sharper corner, so WYDOT will reduce the speed through the area to make it safer for drivers. The permanent roadway design will provide an adequate foundation and reduce weight. 

How is WYDOT making sure the new permanent alignment will be safe?
WYDOT geologists will continue to map, assess, and investigate the area, and additional mitigation measures will be taken to lessen the risk of failure. WYDOT engineers, geologists and planning personnel are currently researching numerous potential options for what that will look like.  

Will the detour and new alignment improve drainage in the area?
Yes, stormwater drainage evaluations are a standard part of construction and will continue to be evaluated. The appropriate measures will be in place to ensure proper drainage for the temporary detour and future reconstruction.  

The design of the detour addressed drainage improvements by contouring the fill to ensure no ponding of water and allowed water flows to be directed away from the temp detour. The existing contours of the original alignment lend to surface run-off to be naturally carried away from the fill. The 1969 engineers conveniently placed the roadway that did not require culverts for drainage. As an analogy, they placed the road fill at the continental divide where water to north drains one direction and the water to the south drains the opposite direction.

Why didn't WYDOT address this slide sooner?
WYDOT has been monitoring this creeping slide for decades.  This road section of road was re-paved in 2004 and patched last fall after slow, consistent creep over the past 20 years.  Most recently, WYDOT's geologists installed an inclinometer, a device that measures subsurface slide movement, in the fall of 2023 to monitor this area. Prior to this incident, the slide moved less than an inch per year. A perfect storm of rain early in the week, followed by a rise in daily temps, and overnight temps above freezing resulted in rapid snow melt that saturated groundwater conditions which exponentially sped up this slide movement to the failure we saw June 8. There was no indication of possible failure as this slide did not move quickly for decades.


WYDOT Media Kits

WYDOT will publish media kits here as available.

WYDOT gives full permission for media outlets to use the photo, video, text and other media on this page in their reporting. Please credit all media to WYDOT. 

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Big Fill slide - Teton Pass critical failure - June 2024


Big Fill slide information

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Wyoming Highway 22/Teton Pass suffered a critical failure at milepost 12.8 the weekend of June 8. The highway reopened with a temporary detour on June 28.

Check out the timeline of events using the press releases linked below. We add to this page frequently, check back for updates. 

WYO 22 also experienced a mudslide at milepost 15, which is not related to the Big Fill slide. The slide was discovered June 7. Crews have installed culverts in the area. 

Press Releases:

Additional Facts:

Crews with Evans Construction worked around the clock to build the temporary detour. Crews with Ames Construction are working on the permanent fix.

Governor Mark Gordon issued an emergency declaration June 8. You can read that declaration here. 

Click here for more information about landslides in Wyoming from the Wyoming Geological Survey.

Yellowstone National Park and Grand Teton National Park remain open for visitors. 

Teton Pass sees an Annual Average Daily Traffic (AADT) of almost 10,000 vehicles per day in certain locations along the pass. Summer highs can reach 15,000 vehicles. 

No employees, contractors or other members of the public were injured in the collapse. 

No equipment or buildings were lost or destroyed in the collapse. 


Big Fill Slide Photos

WYO 22 - minor cracking - June 6 - photo 1 (61.83  KB)
WYO 22 - minor cracking - June 6 - photo 2 (18.44  KB)
WYO 22 - minor cracking - June 6 - photo 3 (17.85  KB)
WYO 22 - minor cracking - June 6 - photo 4 (9.5  KB)
WYO 22 mudslide - milepost 15 - June 7 - drone photo 1 (3.98  MB)
WYO 22 mudslide - milepost 15 - June 7 - drone photo 2 (4.05  MB)
WYO 22 mudslide - milepost 15 - June 7 - drone photo 3 (4.41  MB)
WYO 22 mudslide - milepost 15 - June 7 - drone photo 4 (4.33  MB)
Big Fill slide - crack before slide - June 7 - photo (1.09  MB)
Big Fill slide - June 8 - drone photo 1 (4.52  MB)
Big Fill slide - June 8 - drone photo 2 (4.85  MB)
Big Fill slide - June 8 - drone photo 3 (4.61  MB)
Big Fill slide - June 8 - drone photo 4 (4.54  MB)
Big Fill slide - June 8 - drone photo 5 (4.66  MB)
Big Fill slide - detour underway - June 10 - drone photo 1 (4.44  MB)
Big Fill slide - detour underway - June 10 - drone photo 2 (4.62  MB)
Big Fill slide - detour underway - June 10 - drone photo 3 (4.64  MB)
Big Fill slide - detour underway - June 10 - drone photo 4 (4.62  MB)
Big Fill slide - Geology drilling - June 11 - photo (5.5  MB)
Big Fill slide - Evans Construction detour progress - June 11 - photo (7.75  MB)
Big Fill slide - Evans Construction detour progress - June 11 - photo 2 (3.37  MB)
Big Fill slide - detour work - June 12 - drone photo (4.73  MB)
Big Fill slide - detour work - June 12 - drone photo 2 (4.68  MB)
Big Fill slide - detour work - June 13 - drone photo (2.18  MB)
Big Fill slide - detour work - June 13 - drone photo 2 (2.22  MB)
Big Fill slide - detour work - June 14 - drone photo (4.55  MB)
Big Fill slide - detour work - June 15 - drone photo 1 (4.42  MB)
Big Fill slide - detour work - June 15 - drone photo 2 (4.41  MB)
Big Fill slide - detour work - June 16 - drone photo 1 (4.46  MB)
Big Fill slide - detour work - June 16 - drone photo 2 (3.98  MB)
Big Fill slide - detour work - June 16 - drone photo 3 (4.05  MB)
Big Fill slide - detour work - June 17 - drone photo 1 (3.94  MB)
Big Fill slide - detour work - June 17 - drone photo 2 (4.12  MB)
Big Fill slide - detour work - June 17 - drone photo 3 (4.24  MB)
Big Fill slide - detour work - June 18 - drone photo 1 (4.74  MB)
Big Fill slide - detour work - June 18 - drone photo 2 (4.59  MB)
Big Fill slide - detour work - June 19 - drone photo (4.39  MB)
Big Fill slide - detour work - June 20 - drone photo 1 (4.38  MB)
Big Fill slide - detour work - June 20 - drone photo 2 (4.66  MB)
Big Fill slide - detour work - June 21 - drone photo 1 (4.46  MB)
Big Fill slide - detour work - June 21 - drone photo 2 (4.31  MB)
Big Fill slide - detour work - June 22 - drone photo (4.48  MB)
Big Fill slide - detour work - June 23 - drone photo 1 (4.74  MB)
Big Fill slide - detour work - June 23 - drone photo 2 (4.63  MB)
Big Fill slide - detour work - June 24 - drone photo 1 (4.68  MB)
Big Fill slide - detour work - June 24 - drone photo 2 (4.59  MB)
WYO 22 mudslide - mile marker 15 - June 24 - culvert install (4.65  MB)
Big Fill slide - detour paving - June 25 - drone photo 1 (4.48  MB)
Big Fill slide - detour paving - June 25 - drone photo 2 (4.74  MB)
Big Fill slide - detour final touches - June 26 - drone photo 1 (4.14  MB)
Big Fill slide - detour final touches - June 26 - drone photo 2 (4.1  MB)
Big Fill slide - detour final touches - June 27 - drone photo 1 (4.33  MB)
Big Fill slide - detour final touches - June 27 - drone photo 2 (4.21  MB)
Big Fill slide - detour complete - START bus - June 28 - photo (173.74  KB)
Big Fill slide - Detour open - June 28 - drone photo (1.19  MB)
Big Fill slide - Detour open - June 28 - drone photo 2 (1.02  MB)
Big Fill slide - long term fix - Aug. 12 (2.17  MB)
Big Fill Slide - long term fix - Sept. 16 - drone photo (4.32  MB)
Big Fill slide - long term fix - Sept. 16 - drone photo 2 (4.39  MB)
Big Fill slide - long term fix - Sept. 24 - drone photo (4.75  MB)
Big Fill slide - long term fix - Oct 9 - drone photo (4.17  MB)
Big Fill slide - long term fix - Oct 9 - drone photo 2 (4.35  MB)

WYDOT gives full permission for media outlets to use the photo, video, text and other media on this page in their reporting. Please credit all media to WYDOT. 


VIDEO - Big Fill Reconstruction

Work to reconstruct WYO 22 at the site of the Big Fill slide in Teton County has entered a new stage. (published Sept. 25, 2024)


VIDEO - WYDOT Report: Big Fill Landslide Response

The morning of June 8, a landslide destroyed a segment of WY 22, severing a major commuter route between Jackson and Idaho. WYDOT has been working to reopen the road to traffic by building a temporary detour. Featuring: Bob Hammond, WYDOT Resident Engineer - Jackson


VIDEO - Big Fill Slide detour progress - June 8 to June 17

Please credit WYDOT.

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