Learn and Explore
Updated: August 24, 2021
The Pretty Rocks Landslide, which underlies the roadbed at Mile 45.4 of the of the Denali Park Road, traverses a precipitous slope near Polychrome Overlook. It is one of several known landslides in the area and one of the more than 140 mapped unstable slopes along the entire Park Road. National Park Service (NPS) monitoring data indicate that the rate of movement in this area has increased dramatically in recent years.
Pretty Rocks Landslide Comparison (November 2019 vs January 2020)
The Pretty Rocks landslide is more accurately described as a rock glacier. Rock glaciers are closely related to glaciers, but they contain much more rocky debris with ice in the pore spaces. The average annual temperature shift of the area to above freezing in recent years is believed to be causing the rock glacier to thaw, resulting in the recent acceleration of the landslide.
Next StepsLast updated: August, 2021
In May 2020, NPS and FHWA partnered to conduct an Expert-Based Risk Assessment (EBRA) that evaluated the geotechnical attributes of several alternatives, including north and south re-routes and a mainline option. Informed by the EBRA, a value analysis was conducted in July 2020 to determine which alternative provided the greatest value.
Based on the outcomes of the EBRA and value analysis, FHWA recommended the mainline option that would retain the existing road alignment. In collaboration with FHWA, the NPS will address maintaining road access west of Polychrome Mountain in two stages:
History of the "High Line"
The Alaska Road Commission (ARC) began to build the trans-park road into Mount McKinley National Park in 1922. Over the course of 16 years, crews carved a road out of wilderness. During this time, the National Park Service decided to place part of the road along the side of Polychrome Mountain—the "High Line."
Learn more about how and why the High Line became the park road route.
Pretty Rocks Landslide Comparison (September 2018 vs March 2019)
Last updated: August 27, 2021