OF-06-01 Rockfall Hazards Susceptibility in the Estes Valley Development Code Area, Estes Park, Larimer County, Colorado

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Citation: Wait, T. C., and Karen A. Berry. “OF-06-01 Rockfall Hazards Susceptibility in the Estes Valley Development Code Area, Estes Park, Larimer County, Colorado.” Rockfall Hazard. Open File Reports. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 2006.

Description

Describes the potentially hazardous rockfall areas within the Estes Valley Development Area in Larimer County. The CGS worked with the Town of Estes Park planning department to develop Geographic Information System (GIS) coverages for potential rockfall hazard areas in 2003. The resulting map data has been compiled into this publication for use by planners, geologists, engineers, and public users. This publication includes a 1:24,000 map of the GIS data and a description explaining the hazard, mapping methodology, and implications to development in the area. Digital ZIP/PDF download. OF-06-01D

Rockfall is considered a geologic hazard in the Colorado Revised Statutes (C.R.S. § 24- 65.104), and local communities are encouraged to identify rockfall hazards and adopt land-use policies to regulate development in rockfall prone areas. This publication identifies these areas and describes the methods used to determine rockfall susceptibility within the Estes Valley Development Code Boundary.

Rockfall occurrences are difficult to predict, and can range from a single rock falling or rolling to large-scale catastrophic events. The size of the falling rock depends on the source area geology (bedding thickness, bedding dip and dip direction, hardness, jointing/fracturing orientation), weathering, and position. Rolling or sliding rocks occur on steep slopes where loose rocks may mobilize from gravity (slope creep) or hillside development activity. This may occur in areas where loose rocks are located on steep slopes, regardless of the presence of an outcrop.

Rockfall events can quickly demolish structures and injure or kill people in the rockfall path. Rocks falling on highways may strike vehicles, block traffic, or cause accidents and road damage. However, most areas susceptible to rockfall can be identified and steps can be taken to avoid, reduce, or mitigate rockfall risk.