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• -3- • <br />due to the gravelly nature. The fines in the soil consist mainly of silts and <br />clays, This gravel unit appears to be fairly sell-consolidated and thus the <br />risk of side-wall collapse is low. Y,owever, there were observed a few poorly <br />consolidated areas and the risk of collapse in these small areas is presumed <br />to be slightly higher. The Soil Conservation Service (SCS) classifies this <br />soil in Class IIIe (see notes), <br />,~'P.`i}'~'B~D SI'ALiS (Bedrock Unit) <br />This unit is sho~m by the blue areas on the map. This unit forms the slopes <br />of the mesas and is the prospective bedrock on the site. The contact between <br />the gravel unit and the shale unit was observed on the west point of the <br />"elongated mesa" (Phase 5), the east side of the "elongated mesa" (Phase 3) <br />and in the process area. Outcrops of the shale can be observed throughout <br />this area. This shale covers approximately 50 acres (thickness unknown). <br />The shales in this area are presumed to be [•;ancos Shale, Nancos Shale is <br />typically described as a thin-bedded, marine shale with fine-grained sandstone <br />and limestone lenses present throughout. This shale has been known to <br />exhibit swelling characteristics due to bentonitic layers. Locally, this <br />shale is light to medium gray in color. It is highly weathered to loosely <br />consolidated, 'crumbly' debris. therefore, the slope stability is presumed <br />to be low. The unit appears to dip gradually to the northeast, but an <br />accurate strike dip reading is not possible due to the highly weathered <br />condition. Ilhite lime "splotching" was abundant on the surface. The shale <br />in the pit area appears to be highly gypsiferous. [zany specimen of crystalline <br />gypsum ~rere collected on the surface. The gypsum is more resistant to <br />xeathering than the shale and therefore impales. <br />ALLU'JIAL G.RAVisLS ('Erosional Debris) <br />This unit is not an official geologic unit and is not shotim on the map, but <br />could be of econcmic signifigance to the mining operation. It contains <br />the larger gravels and pebbles of the gravel unit described above. It is <br />the erosional debris of the gravelly unit and is intimately mi:ced with the <br />weathered top of the shale unit. It ranges in thickness fron a fear inches <br />to several feet. It covers approximately half of the area sho~m as shale <br />on the map and appears on many of the hillsides and in all of the drainages <br />in the area. It is thickest in the drainages and thinnest on the slopes. <br />Its properties are a combination of the gravel unit and the shale unit <br />described above. It is mainly broim-gray in color but also exhibits a <br />'mottled' appearance. Because of its erosional nature, it is presumed to <br />be highly unstable. <br />