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<br />~ 26 - <br /> <br />sist of stacks of loose, joint-bounded blocks which are precariously <br /> <br />unstable when undercut by erosion (figures 12, 14, 15, 16). This <br /> <br />situation gives rise to the constant minor rockfalls which can be <br /> <br />precipitated by a gust of wind or another falling rock. Evidence of <br /> <br />larger scale instability in the cliffs can be seen in the weathered <br /> <br />and open joints which, in many cases, form fissures several tens of <br /> <br />feet back of the cliff face (figures 13, 17). These are especially <br />prominent in projecting points in the cliff which form between adja- <br /> <br />cent gullies. Such gullies or re-entrants in the c1iff1ine tend to <br /> <br />follow minor faults which are oriented at approximate right angles to <br /> <br />the cliff1ine. The precipitous gullies on Gallo Bluff, and also those <br /> <br />in the Carbonate Creek watershed that lie between the north end of <br /> <br />the bluff and Elk Mountain, are locally choked with coarse rock rubble <br /> <br />at a precarious angle of repose. The currency and active nature of <br /> <br />cliff retreat is shown by still-green trees that can be seen along with <br /> <br />rubble in the steep gullies (figure 12). <br /> <br />Avalanches and Potential Debris Slides on Elk Mountain (3b) <br />The area extending north from the barren cliffs of Gallo Bluff to <br /> <br />the vicinity of Elk Mountain is similar in structure and composition <br /> <br />to Gallo Bluff. Slopes are nearly as steep but the area is covered <br /> <br />with small timber and brush which indicates somewhat less active mass <br /> <br />wasting. In general, there is a fairly stable cover of a few tens of <br /> <br />feet of unconsolidated colluvial soils overlying the Cretaceous shale <br /> <br />and sandstone beds. This area is within the Carbonate Creek drainage <br /> <br />basin and is drained by numerous precipitous ravines which have cut <br /> <br />through the coarse colluvial soils, and flow on the exposed shale and <br />