OF-06-02 Rockfall Hazards Susceptibility in the Evergreen Area, Jefferson County, Colorado


Describes potentially hazardous rockfall areas with the Evergreen Community Plan area in Jefferson County. The CGS worked with the Jefferson County Planning Department to develop Geographic Information System (GIS) coverages for potential rockfall hazard areas in 2004. The resulting map data has been compiled into this publication for use by planners, geologists, engineers, and public users. Included are 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-06-02D

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 study area. The study area includes (approximately) the part of Jefferson County east of the Clear Creek County Line, west of R70W, north of N. Turkey Creek and south of Genesee Park.

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.