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Case Study - Colorado

Programmatic Agreement Addresses the Cumulative Effects of Rockfall Mitigation Projects on the Georgetown-Silver Plume National Historic Landmark District.


Interstate 70 is the primary transportation corridor traveling east-west through the state of Colorado, passing through the Rocky Mountains and a series of historic mining towns. A two mile stretch of Interstate 70 above the town of Georgetown exhibits particularly steep slopes that create significant rockfall hazards for the traveling public. Rockfall mitigation projects have been completed in this corridor annually since 2000, and the Programmatic Agreement (PA) will help streamline the Section 106 review process for upcoming projects, including the installation of rockfall attenuators on the slope above the highway and other rockfall prevention measures. All work for the future projects will take place within the boundary of the Georgetown-Silver Plume National Historic Landmark (NHL) District. The Colorado Department of Transportation (CDOT), in consultation with the Federal Highway Administration (FHWA) and State Historic Preservation Officer (SHPO) determined that these rockfall mitigation projects will result in a cumulative adverse effect on the landmark district. The installation of rockfall mitigation structures along this stretch of highway creates a visual effect that has modified the appearance of Georgetown Hill within the boundary of the NHL district.


National Historic Landmarks are properties recognized by the Secretary of the Interior because they possess exceptional value or quality in illustrating or interpreting the heritage of the United States. The Georgetown-Silver Plume National Historic Landmark District comprises the Town of Georgetown, the Town of Silver Plume, and the Georgetown Loop Historic Mining & Railroad Park between the two silver mining towns along Clear Creek, in Clear Creek County, Colorado. Despite the construction of I-70 through the district in the 1960s, the NHL includes the entire commercial and residential areas, with well preserved examples of the buildings and mining structures of the Colorado Silver Boom from 1864 to 1893.


The PA was developed by CDOT and FHWA, in consultation with the USDA Forest Service, the Town of Georgetown, Town of Silver Plume, Clear Creek County, Colorado Historical Society, and the Georgetown Silver Plume Historic District Public Lands Commission. The National Park Service, Intermountain Region was invited to participate in consultation because of the program’s effects on the National Historic Landmark District. In addition, FHWA invited the ACHP to participate in consultation because the PA is for a continuing program that affects a NHL district. The ACHP’s role was to assist with the development of the PA, identifying streamlining measures acceptable to the parties. The PA provides that rockfall mitigation projects on Interstate 70 within the NHL District may proceed after CDOT (1) provides documentation of the proposed project and a proposed treatment plan to the consulting parties; (2) provides each consulting party 30 days to review and comment on the documentation provided, and (3) takes into account any comments in finalizing the treatment plan. The PA also establishes guidelines for CDOT’s use in selecting paint colors for rockfall containment systems (in order to blend with the natural landscape); and requires CDOT to develop interpretive materials about the relationship between the geology of the surrounding landscape and the historic mining industry.  


The PA is a rare example of a programmatic approach to dealing with incremental impacts to a historic district that, while individually minor, have a long-term, cumulative effect on the Georgetown Silver Plume National Historic Landmark District. All parties agree on the need to install rockfall mitigation projects on the steep slopes of Georgetown Hill. Standardized measures for minimizing the visibility of these projects and the development of interpretive materials such as signage or brochures are relatively simple and inexpensive to implement, and should be effective. This program demonstrates that the consideration of cumulative effects on historic properties can be addressed, at least in some circumstances, using a Section 106 Programmatic Agreement. 

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Updated May 28, 2009

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