The Bridger-Teton National Forest has closed the Greys River Road (FS Road 10138) to all activity until further notice, from the parking lot in Alpine, Wyoming through the Porcupine Road as a result of the Porcupine Landslide which began in February, 2018.
“We have finished analyzing the modeling that has been completed on a potential flooding scenario,” said Greys River District Ranger Justin Laycock. “While the model shows that the flooding risk to homes or property in Alpine, Wyoming is considered ‘low’ and limited to two structures, the risks in the corridor itself are much different,” he explained. “The model looked at a 40-foot high natural dam completely occluding the Greys River. In the model, if the dam was to back up water to the point it breeched the natural dam or the natural dam gave way, the low lying areas of the Greys River corridor could experience up to a 10-foot wall of water,” he said. “Given the uncertainty of when or if the scenario could take place, and the fact that the ability to notify and clear the acres of affected area in the modeled scenario would take longer than the 4 hours we would have to act, we must close the area to human presence until the situation stabilizes,” he said.
The landslide is a quarter of a mile wide and is still slumping towards the Greys River. The Forest worked with the U.S. Army Corps of Engineers (USACE) on modeling the flood scenario should the landslide create a natural dam in the Greys River. “The predicted rain and warm up that is characteristic of the beginning of spring runoff has reached one of our established trigger points and is the reason for my decision to close the corridor immediately” Laycock said.
With the closure order, two of the Forest’s Guard Stations which are usually available to rent, the McCain and Deer Creek Guard Stations, will be unavailable for reservations until further notice.
Although the Alpine access and the Greys River Corridor is closed through Porcupine Road, visitors still may access the Forest beyond the closure by three other routes. (1) either by the Smith’s Fork, Forest Service Road 10072, road located South of Afton or (2) through forest service access from Big Piney, WY (proceed to Ryegrass Junction to Forest Service Road 10125, also known as N. Cottonwood, then over McDougal Gap to Greys River Road) and (3) The La Barge Road accessed from the town of La Barge, Wyoming. “There is quite a bit of country still open and accessible upstream of the landslide but the area downstream is going to remain closed until further notice,” he said.