Geologically hazardous areas include areas susceptible to erosion, sliding, earthquake, or other geological events.  They pose a threat to the health and safety of citizens when incompatible commercial, residential, or industrial development is sited in areas of significant hazard.  Geologically hazardous areas also have an important function in maintaining habitat integrity.  Mass wasting, landslides, and debris flows contribute needed sediment and wood for building complex instream habitats, estuarine marshes, and beaches important for fisheries, wildlife and recreation.  At the same time, mass wasting events can harm habitat and lead to the need for stream restoration.

 

Some geological hazards can be reduced or mitigated by engineering, design, or modified construction or mining practices so that risks to health and safety are acceptable.  When technology cannot reduce risks to acceptable levels, building in geologically hazardous areas is best avoided.  This distinction should be considered by counties and cities that do not now classify geological hazards as they develop their classification scheme.

 

Areas that are susceptible to one or more of the following types of hazards should be classified as a geologically hazardous area:

·         Erosion hazard (including river and coastal streambank erosion areas and channel
          migration areas).

·         Landslide hazard.

·         Seismic hazard.

·         Areas subject to other geological events such as coal mine hazards and volcanic hazards
          including:  mass wasting, debris flows, rock falls, and differential settlement.

 

Counties and cities should consider classifying geologically hazardous areas as either known or suspected risk, no risk, or risk unknown where data are not available to determine the presence or absence of a geological hazard.