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Ralston Quarry Slope Stability <br /> INTRODUCTION <br /> The project site is underlain generally by bedrock of the Pierre Shale on which residual <br /> (weathered in place) and colluvial ("slope wash") soils have developed. The clay and silt <br /> shales of that formation, however, were intruded by a sill of shoshonite, a dark gray, <br /> igneous rock. <br /> The Asphalt Paving Company has mined aggregate from that shoshonite sill exposed on <br /> the eastern side of a north-trending ridge in Jefferson County north of Golden for several <br /> decades. The mining property straddles the ridge with Ralston Reservoir occupying the <br /> drainage to the west of the mining property and Upper Long Lake immediately to the <br /> east. The relative positions of these features can be seen in an historical Google Earth® <br /> images below. <br /> > F <br /> t <br /> ter.. f <br /> w <br /> Asphalt Paving Co. site Area of Tailings Placed on West-facing Slope <br /> Actual mining has been from the eastern side of the ridge. We understand that until <br /> approximately 20 years ago, tailings from the mining on the east side of the ridge were <br /> placed as fill on the west-facing side. The filled slope was graded at an approximately <br /> 2'/2 : 1 (horizontal : vertical) angle. In the early 2000's, several retention ponds also <br /> Job No. 18-3046 GROUND Engineering Consultants, Inc. Page 2 <br />