"Landslide incidence" is a measure of how frequently landslides occur in any given area. This map shows areas of high landslide incidence in deep red. In these areas, over 15% of the earth's surface is either an active landslide or an historic landslide. Areas of high landslide incidence usually have at least two of the following three risk factors: 1) steep slopes, 2) slide prone soils, or, 3) high precipitation. As you can see, the mountainous and high precipitation areas of the west coast have many areas of high incidence as do many parts of the Rocky Mountain area. Areas shown in orange have a moderate landslide incidence.
This map also shows "landslide susceptibility" (the probable degree of response of near-surface rocks and soils to natural or artificial excavation, loading of slopes, or unusually high precipitation The pink and brown colors used on the map have high landslide susceptibility. In these areas, at least 15% of earth's surface has all of the risk factors associated with an elevated landslide hazard but landslide incidence is not high.
The map is a portion of the Landslide Overview Map of the Conterminious United States (USGS Special Paper 1183). This paper and others can be accessed via the web at the USGS Geologic Hazards website.