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<br />subsequently in greater detail. <br /> <br />Unconsolidated debris ill available on slopes within the drainage basins <br /> <br />on steep slopes ranging from approximately 250 to 400 thus satisfying conditions <br /> <br />(1) and (2). This material is derived primarily from weathering of the <br /> <br />Maroon Formation that is described ~y Robinson (1975) as a grayish-red <br /> <br />to reddish-orange siltstone and silty sandstone and grayi sh-red, pale red <br /> <br />and pale red-purple arkosic :;andstone. <br /> <br />The weathering of this formation <br /> <br />produces a heterogeneous mixture of largl= blocks of sandstone and clay- <br /> <br />and silt-rich soils that lie in metastable** positions on steep slopes <br /> <br />and In gullies. During intenEle precipitation events such as that of July <br /> <br />24, 1977, the metastable equilibrium is upset and the soil, rock, and organlc <br /> <br />material slides, flows, and avalanches do\tn1s1ope into larger gullip-s within <br /> <br />the basin. These gullies have lesser gradients, usually 150 to 250, and <br /> <br />as a result the debris movement stop~:; momentarily, the central channels <br /> <br />become blocked, and flood water from higher in the basins becomes temporarily <br /> <br />impounded behind the debris dams. As described in the following chapter, <br /> <br />this may result in the formation of debris flows. Additional debris in <br /> <br />the basins is derived from weathering of the Eagle Valley Evaporite, a <br /> <br />white to medium-gray gypsum and associated grel~nish-gray claystone, siltstone, <br /> <br />** Metastable: Refers to a condition of stability which is maintained <br />under only a limited set of conditions and may be easily upset to <br />become an unstable co'ndition.' <br /> <br />- 7 - <br />