At Mile 45.4 of the Denali Park Road, the Pretty Rocks landslide traverses a precipitous slope high on the side of Polychrome Mountain. The Landslide is one of several known geologic hazards in the area and is threatening the integrity of approximately 300 linear feet of the Park Road. Monitoring data indicates that this area's rate of movement has increased dramatically in recent years and current maintenance efforts are not sustainable in the face of continued and accelerating movement. Left unaddressed, the Pretty Rocks landslide would continue displacing the road, eliminating road access to the western half of the Park Road and popular visitor destinations and facilities including Toklat Road Camp, the Eielson Visitor Center, Wonder Lake, and businesses in the Kantishna area.
In 2020, NPS and FHWA partnered to conduct an Expert-Based Risk Assessment (EBRA) and a value analysis (VA) that evaluated these alternatives, including north and south re-routes and a mainline option that would retain the existing road alignment. NPS identified four criteria to use for evaluating the options: feasibility of construction, continuity of access during and after construction, resiliency / life cycle, and how it supports the Denali NP mission statement. Based on the outcomes of these expert panels, FHWA recommended the mainline option, which included building a bridge across the Pretty Rocks Landslide. NPS formally accepted their recommendation and is moving forward with the design and environmental assessment of the "Polychrome Area Improvements" project to maintain the road in place:
Phase I: Construct a 400-foot launchable modular steel truss bridge spanning the Pretty Rocks landslide
Phase II: Address four additional geological hazard sites, including Bear Cave slump, with a combination of engineered solutions to mitigate rockfall
For more information about the Pretty Rocks Landslide and the Polychrome planning process, please visit the Denali National Park and Preserve's website: https://www.nps.gov/dena/learn/nature/pretty-rocks.htm https://www.nps.gov/dena/getinvolved/polychrome-plan.htm
Outdoor Recreation Planner
Denali National Park and Preserve
Denali National Park and Preserve is proposing improvements to the Park Road in the Polychrome Area to address several geologic hazards, including the Pretty Rocks Landslide, that are jeopardizing public safety and infrastructure. The project will focus on engineered solutions along approximately two miles of the Park Road (mile 44-46).