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• EXPLANATION OF MAP UNITS <br />lsl LANDSLIDE: A landform resulting from the moderate to <br />ls= rapid, downward and outward movement of rock and/or <br />ls~ soil where there is a surface of rupture or zone of <br />weakness that separates the landslide from more stable <br />underlying material. Landslides, including earthflows, <br />result from the mass movement of rock and/or soil in <br />response to gravitational stresses and these movements <br />may affect adjacent downslope areas. Natural or man- <br />caused disturbance of landslide areas could initiate <br />additional instability and mass movement. Relative age <br />of landslides is indicated by subscripts (1 is the <br />youngest). <br />mf MUDFLOW: an area subject to the rapid downslope <br />movement of wet, viscous masses of fine-grained <br />material following mobilization of the material by <br />intense rainfall or snow-melt runoff. Mobilization <br />usually includes the erosion and transport of poorly <br />consolidated surficial materials that have accumulated <br />in a drainage basin and its channels. Physiographic <br />features associated with the mapped mudflow areas <br />suggests recent mudflow activity and danger for any <br />structures placed in the mudflow areas. <br />da DEBRIS AVALANCHE: elongate chute-like landforms that <br />are produced by very rapid sliding and flow of unsorted <br />mixtures of soil and rock material down relatively <br />steep slopes. Debris avalanches occur during periods <br />of intense rainfall, may traverse long distances as <br />debris flows over gentle slopes below mountainous <br />areas, and usually are associated with rockfall areas. <br />Nearly unpredictable in time, debris avalanches are a <br />severe hazard for many land uses. <br />rf ROCKFALL: an area subject to rapid, intermittent, <br />nearly unpredictable rolling, sliding, or free falling <br />of detached bedrock of any size from a cliff or very <br />steep slope. Rockfall areas most commonly occur on <br />sparsely vegetated areas having jointed bedrock cliffs <br />and are a serious hazard for residential development <br />and road construction. <br />dfl DEBRIS FAN: a triangular-shaped landform resulting from <br />dfz the accumulation of water-transported rock, soil, and <br />vegetation debris usually at the confluence of a <br />tributary stream with a larger drainage. Debris <br />accumulation generally is associated with high-density, <br />rapid debris flows that are caused by periodic intense <br />rainfall. These flows may cause severe damage to or <br />• destruction of man-made structures. Relative age of <br />debris fans is indicated by subscripts (1 is the <br />youngest). <br />P6RXI711PPLZCA'fI011 EXH-12 - 2 - <br />