Rockfalls, small landslides, and debris flows are potential hazards on and immediately adjacent to steep slopes. The mass movement of material on steep slopes is typically triggered by intense or prolonged periods of precipitation (Christenson and others,)978). Debris flows are viscous slurries of sediment and water that can transport large boulders substantial distances downslope. In southern and central Arizona, nearly all of the documented historical debris flows have been restricted to mountain slopes and valleys. Rockfalls and landslides are potential hazards below bedrock cliffs and where bedrock outcrops exist at or near the top of steep mountain hillslopes. The existence oflarge boulders near the base of a steep slope should be considered evidence of potential rockfall hazard in most cases.
Potential rockfall hazards in the Cave Creek quadrangle are greatest on or near the toes of slopes of bedrock hills and low mountains formed on granitic rocks (Yg). Rockfall hazard exists in these areas because of the combination of steep slopes and large rock masses exposed on the slopes, and boulders strewn near the bases of these slopes are clear evidence of past rockfalls (Kenny, 1986). Smaller-scale rock falls and slides of groups of smaller rocks may occur on steep hillslopes formed on Precambrian metamorphic rocks or basin-:fi1l deposits (Kenny, 1986). Debris flows may be a hazard along the steep upper reaches of the streams that drain the hills and mountains of the quadrangle. They are typically generated by mass movements on hillslopes or within steep stream valleys. Larger debris flows in some environments may continue downslope out of the mountains and impact piedmont areas. In this environment, however, it is more likely that debris flows will impact only hillslopes and channels within steep-walled mountain valleys.