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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />2"5') <br />00 0" <br /> <br />YAMCOLO <br />GEOTECHNIC DATA <br /> <br />General. <br />The bedrock, or base formation in the area of the proposed Yamcolo <br />Dam is the Mancos Shale. At the dam site, the bedrock is overlain <br />by a thick overburden, transported from two main sources: <br />, 1. Glacial moraine, which was transported down the river basin <br />and which covers the right abutment borrow area and most of <br />the foundation area. <br />2. Mudflow outpouring from Coal Creek which was deposited <br />in several stages and which covers the left abutment, spillway <br />area and a portion of the foundation area. <br />The glacial activity has intermixed some lava-rock and sandstone <br />with the soils derived from the shale. The greatest portion of <br />the glacial soils in this area are therefore moderately tight silty <br />clays with gravels, cobbles and boulders intermixed. The manner in <br />which this material was deposited has resulted in a soil very <br />heterogeneous in nature varying from the tight silty clays of shale <br />derivation in most areas to silts and sands in certain locations. <br />The Coal Creek mudflow material is also derived from the shale and <br />consists predominately of shale chunks with some sandstone in a <br />tight clay matrix. The matrix material consists of a moderately <br />fat clay and provides an impervious blanket. <br /> <br />Exploration <br />Exploration programs have been performed at various times by several <br />entities since 1935. Results of the most recent one are presented <br /> <br />-1- <br /> <br />, <br />'. <br />