The gas well pad near the terminus of the West Salt Creek rock avalanche (flow direction right to left), Mesa County, Colorado, May 2014. Photo credit: Colorado Geological Survey.


A landslide is a sudden mass movement of soil, artificial fill, and/or rock down a slope. Landslides include many different kinds of mass movements, including falls, topples, slides, spreads, flows, or a combination of one or more of these movements. Slopes of almost any angle, from slight hills to steep mountains, can fail in a sudden landslide. Landslides can be small or very large, up to thousands of cubic feet, can travel incredibly quickly (faster than a person can run), and may recur multiple times in virtually the same location.

Because landslides of any size may threaten people and infrastructure, it is important to understand where and how landslides occur and how they may affect future development. Colorado experiences many landslides each year because of its steep terrain. Some of them occur in remote areas that are difficult to monitor, with most occurring west of the Front Range to the Western Slope. Damage from landslides in Colorado is estimated to be millions of dollars per year. A large rockfall or landslide can dam a river, cover or damage roads, knock bridges off their abutments, or crash into moving traffic. Landslides can also present serious threats to buildings and homes built in slide paths.

As a a widespread and active geologic hazard in many areas of Colorado, landslides that pose the highest risk to communities, areas, and infrastructure are carefully mapped and inventoried by the CGS. (See additional information in our debris flow section.)

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