Polychrome Area Plan

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Note: This page describes the planning effort for a long-term solution for the Denali Park Road in the Polychrome area. The Planning, Environment, and Public Comment (PEPC) website has details about upcoming public meetings and opportunities to submit comments as part of the compliance process for the proposed project.

Landslide movement at Pretty Rocks (mile 45.4 on the Denali Park Road) has accelerated in recent years and as of September 2021, maintenance efforts are no longer sustainable in the face of such movement. Buses will travel no farther than mile 43 of the 92-mile road until a long-term solution is implemented to restore reliable road access west of the Pretty Rocks Landslide. Denali National Park and Preserve is proposing improvements in the Polychrome Area to address several geologic hazards between miles 44 and 46, including the Pretty Rocks Landslide, that threaten public safety and infrastructure. The project would begin in 2022.

Read more about the science and monitoring of the Pretty Rocks Landslide and other geologic hazards.
a dirt road precariously situated on the side of a mountain
NPS road maintenance staff made an extraordinary effort in Spring 2021 to repair the road at Pretty Rocks

NPS Photo

Planning Process

The collaboration between the National Park Service (NPS) and Federal Highways Administration (FHWA) to develop a long-term solution for the Park Road in the Polychrome Area began in the winter of 2017–2018. FHWA brainstormed several conceptual ideas, ruled them out one-by-one through preliminary evaluation, and narrowed it down to three alternatives for further consideration: bridging the landslide, removing the upper landslide, and detouring around the landslide. 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 National Park mission statement.

In 2019, FHWA conducted geotechnical investigations at Pretty Rocks and confirmed that the rock mass strength of the material at the east and west abutments was sufficient to support a bridge so bridging the landslide was retained as a viable alternative. Further analysis determined that removal of the upper landslide would cause the slope to become unstable again in 10–15 years due to the continuous exposure of the weak ash layer, so it was eliminated as a long-term solution.

In 2020, NPS and FHWA partnered to conduct an Expert-Based Risk Assessment (EBRA) and a Value Analysis (VA) that evaluated the remaining alternatives, including north and south re-routes and a mainline option that would retain the existing road alignment. Based on the outcomes of these expert panels, FHWA developed the Polychrome Project Delivery Plan and recommended the mainline option, which included building a bridge across the Pretty Rocks Landslide (mile 45.4) and constructing a retaining wall along the road above the Bear Cave Landslide (mile 44.8). NPS agreed that the mainline option offered several advantages over the re-routes such as retaining more of the historical character and visitor experience, minimizing the impacts to natural resources and wilderness, and restoring reliable access to the western portions of the park in the shortest amount of time. A summary of factors that went into the decision process to dismiss the reroute alternatives is provided in the table below. FHWA moved forward with the design for the bridge and the additional engineering solutions for the mainline option in Fall 2020.
A satellite image of the Polychrome area. Colored lines indicate the southern alignment options (south of the existing road, several new bridges), the mainline option (following the existing road, one new bridge) and northern option (several new bridges).
Potential alignments considered by FHWA and NPS. The orange segments represent bridges.

Source: DG&A 2020

Comparison of Alignments

Factor South Alignments North Alignment Mainline
Construction duration 11 to 13 years 12 to 14 years 1 to 2 years
Number of new bridges 5 to 8 8 1
Length of new road 5 to 6 miles 6 miles 600 feet
Project area in designated wilderness 780 to 830 acres 748 acres 11 acres
Cost $255–$275 million $186 million $91 million
Maintenance gravel need over 50-year design life 1 million cubic yards 1 million cubic yards 25,000 cubic yards

In 2021, additional geotechnical investigation was done to inform the design of the bridge as well as the preliminary design of the retaining wall at Bear Cave Landslide. FHWA provided NPS with preliminary (30%) design plans for a Pretty Rocks bridge. The next step in the planning process is to complete the required compliance, which will assess the potential environmental impacts of the proposed project.
people standing on a gravel road on the side of a mountain
FHWA engineers visited the site of the proposed Pretty Rocks bridge in August 2021

AECOM / Jon Isaacs

Project Overview

Although Pretty Rocks Landslide is the highest priority and would be addressed first, the NPS is proposing a comprehensive approach with several engineered solutions along approximately two miles of the Denali Park Road (Mile 44–46) to ensure that access through the Polychrome area wouldn't be subsequently jeopardized by another nearby hazard. The proposed project is referred to as the “Polychrome Area Improvements” project and has been separated into two phases to expedite the start date of the first phase and allow time to secure funding and finalize designs for secondary phases:

A satellite image of the Polychrome area with colored lines overlaid to mark the boundaries of Phase I and Phase II project work.

Phase I

  • Construction of an approximately 400-foot steel bridge to span the Pretty Rocks Landslide. A temporary platform would be installed on the east side to extend the staging area during bridge construction.
  • Excavation to the east and west of the bridge to accommodate construction activities and traffic. The majority of the excavated material would be placed on the slope below the road.
  • Slight realignment of the road on the west side of the bridge to allow for a proper turning radius for buses and other vehicles getting on and off the bridge.
  • Installation of retaining walls and drainage improvements to the east of the bridge, on the uphill slope.
  • Rock scaling, rock reinforcement, and/or creation of rockfall ditches to reduce rockfall risk.

Phase II

  • Construction of a partially buried retaining wall along 1,000 feet on the south side of the road and drainage improvements above Bear Cave Landslide.
  • Temporary widening of the road above Bear Cave Landslide to accommodate traffic during construction.
  • Rock scaling, rock reinforcement, and/or creation of rockfall ditches to reduce rockfall risk.

The current federal budget proposal allocates $53 million in funding for the continued design and implementation of Phase I, which includes a bridge at Pretty Rocks. Phase I would require approximately five months of excavation plus three months of bridge construction and would take approximately two years to complete. Road access through Polychrome is not anticipated during Phase I. Visitor transportation would be limited to Mile 43 of the Park Road and buses would turn around at the East Fork Toklat bridge or the East Fork Cabin site. Access to Kantishna inholdings would be primarily by air until the bridge is completed.

An additional $65 million would be required to complete Phase II and it would be implemented at a later date. Road access through Polychrome is anticipated during Phase II, likely with some delays or temporary restrictions expected at the construction sites. Visitor transportation to destination points west of Pretty Rocks and regular traffic to Kantishna inholdings would be allowed during Phase II.

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1 minute, 58 seconds

Take a brief tour of the bridge designed for Polychrome, to span the landslide at Pretty Rocks. No audio.


NEPA and NHPA Compliance

The National Environmental Policy Act (NEPA) mandates an environmental assessment (EA) of any proposed federal action that has the potential to “significantly affect the quality of the human environment." Section 106 of the National Historic Preservation Act (NHPA) requires that federal agencies identify and assess the effects its actions may have on historic properties and consider public views and concerns about historic preservation issues when making final project decisions. Compliance with the NHPA will be completed concurrent with, but as a separate process to, the NEPA compliance.

Denali National Park and Preserve has contracted an environmental consulting firm (AECOM) to prepare the EA for the proposed Polychrome Area Improvements project. Environmental and cultural compliance was formally initiated in October 2021 and will be completed by March 2022.

The following steps will be followed for the compliance process:
  • Step 1. Conduct civic engagement (Oct ‘21)
  • Step 2. Identify environmental impacts and assess the effect to historic properties (Oct-Nov ‘21)
  • Step 3. Prepare draft environmental document and select preferred alternative (Nov-Dec ‘21)
  • Step 4. Develop an agreement document with the State Historic Preservation Office (Dec ’21-Jan ‘22)
  • Step 5. Public review of draft environmental document (Jan-Feb ‘22)
  • Step 6. Analysis of public comment (Feb ‘22)
  • Step 7. Prepare final decision document (Feb ‘22)
  • Step 8. Release final decision document to the public (March ‘22)
As part of the civic engagement period, the NPS hosted two virtual public meetings in October 2021 to provide information and answer questions. The goal of these meetings was to identify and document specific concerns, issues, and potential impacts for consideration during the development of the Environmental Assessment. The public was also given the opportunity to submit comments on the project and on the NHPA Assessment of Effects determination. There will be an additional opportunity for public participation and comment following the publication of the draft EA in January 2022: Two virtual public meetings are scheduled to discuss the issues analyzed in the Environmental Assessment and provide information to aid the public in reviewing and commenting on the compliance document.

The Environmental Assessment analyzes a no action alternative and an action alternative. Issue topics considered include cultural resources, wildlife, wetlands / vegetation, noise / soundscape, wilderness, visitor use and experience, socioeconomics, visual / viewshed, and geologic resources.

How Can I Get Involved?

Check the NPS public comment website for updates on public meetings and documents available for review and comment.

If you have questions, please email us.

Public Virtual Meeting

The National Park Service invites the public to learn about the Environmental Assessment of the Polychrome Area Improvements project in Denali National Park and Preserve.

  • Day/Date: Tuesday, January 18th and Wednesday, January 26th, 2022

  • Time: 7:00 p.m. to 8:00 p.m. AKST

  • Location: Virtual, via Microsoft Teams

  • How to attend: The meeting will be held online, and you can join by using any of the options below. On the date of the meetings, please log in early to allow time to resolve technical issues. (Note that it is possible to join these meeting at any time, but nobody'll be there until a bit before 7 pm on the meeting dates!)

Join using a computer or laptop: Click the link for the meeting date above. No download or installation required. Select “Continue on this browser” and choose whether or not to allow the use of your microphone and camera. Type your name as you would like it to appear in the meeting. Then select “join now”.

Join using a tablet or smartphone: Click the link for the meeting date above. Download the Microsoft Teams app from the Apple App Store or GooglePlay. Select “Join meeting”. You do not need to sign into a Microsoft account. Type your name as you would like it to appear in the meeting. Then select “join meeting”.

Join by calling in via phone (audio only):

  • Dial (877) 286-5733 (Toll-free)

  • Enter the conference ID when prompted:

    • 640 654 420# (on January 18th)

    • 256 333 384# (on January 26th)

  • Use *6 to mute and unmute yourself

Public Comments

Comments can be submitted online or in writing and postmarked by February 13, 2022:

Denali National Park and Preserve
P.O. Box 9
Denali Park, AK 99755-0009

Before including your address, telephone number, electronic mail address, or other personally identifiable information in your comments, you should be aware that your entire comment (including your personally identifiable information) may be made publicly available at any time. While you can ask us to withhold your personally identifiable information from public review, we cannot guarantee that we will be able to do so.

Last updated: January 5, 2022

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Mailing Address:

PO Box 9
Denali Park , AK 99755


907 683-9532
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