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land in the valley is located on these terraces. Colluvial <br />• deposits are found along the base of the Grand Hogback where they <br />appear to spread over the terrace deposits. The lower portions of <br />this colluvium can actually be considered alluvial fans, the <br />material of which is derived from shales and sandstones of the <br />hogback. The coarser, more heterogeneous, Colluvial material, <br />gradually becomes finer and more homogeneous as it is carried <br />downslope into the fan-like features. These fans, in turn, grade <br />into the Colorado River Terraces. The contacts between colluvium <br />and terrace were drawn on the basis of the topographic expression, <br />textural changes, and vegetation density, as seen in the color <br />infra-red photographs. <br />Alluvial deposits along this reach of the Colorado River range in <br />thickness from zero, in areas of exposed bedrock, to probably many <br />tens of feet; however, data is not available to establish accurate <br />thicknesses. The terraces are at least 50 feet thick in places, as <br />determined by water wells. Colluvial deposits may be over 100 feet <br />• thick adjacent to steep bedrock slopes. One monitoring hole (OW-3) <br />encountered over 200 feet of Colluvial and alluvial fan material. <br />5.1.3.2 Monitoring <br />Hole Ow-11 monitors terrace groundwater downgradient of the <br />previously proposed disposal area. Water quality information can <br />be found in Appendices 3.3-6 and 3.3-7. Water quality samples have <br />been collected from one surface water site along the Colorado <br />River, downstream from the proposed facilities (Figure 3.3-6 and <br />Appendix 3.3-10). <br />5.1.3.3 Flood-Irrigated Land <br />All land along the Colorado River has the potential for flood- <br />irrigation. Adjacent to and within the permit area (Sections 6 and <br />34), farmland along the southern shore of the river has been flood- <br />. irrigated from the early 1900's to the present by use of the Vulcan <br />NCEC - Coai Ridge #1 5-3 ASC/1145/900301 <br />