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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 />glacier or by melt waters emitted from the glacier. The materials depostted directly by the <br />glacier lack the sorting and bedding characteristic of the stream depostts. The previously <br />mentioned terminal moraine marks a location where the glacier stagnated during retreat, <br />resulting in a thicker accumulation of glacial deposits. Subsequently, the glacier continued <br />tts retreat up the drainage. During the retreat and wasting of the glacier, blocks of ice <br />became detached from the main body of Ice, becoming Isolated in the outwash plain. <br />Sediments were depostted around these Ice blocks. Eventually, the Ice meted, forming <br />depressions in the plain which are referred to as kettles. Small kettle features are present <br />In the area west of Hourglass Reservoir. It is likely that a natural ancestral lake at the <br />location of Hourglass Reservoir was formed in a kettle feature. With the exception of the <br />entrenchment of Beaver Creek and the construction of Comanche and Hourglass Reservoirs, <br />the valley geomorphology has probably changed little since the retreat of the glacier. <br /> <br />5.3.1.2 Bedrock <br /> <br />Bedrock is exposed at the surface or is interpreted to be at a shallow depth on the steeper <br />slopes of the valley walls. The bedrock is identified on the Preliminary Geologic Map of the <br />Greeley I' x 2' Quadrangle (Open Fie Report 78-532) as Precambrian metamorphic rock, <br />felsic and hornblendic gneiss including metabasalt, metatufl, and interbedded metagraywacke <br />wtth local interlayered biottte gneiss. Bedrock is exposed near the southern side of <br />Hourglass Reservoir. The U.S.G.S. map shows a fault in the bedrock at the bottom of the <br />valley to the southwest of the reservoir. This fault Is shown as a splay from a relatively <br />long (about 50 miles) fault that passes near Comanche Peak and has a nearly east-west <br />strike. The fault splay Is Inferred to extend beneath the glacial depostts on the southeast <br />side of the reservoir. <br /> <br />This fault has not been designated as potentially active in the publication "Earthquake <br />Potential in Colorado', 1981 by Kirkham and Rodgers. In this publication, the closest <br />potentially active fault to the project area is the north-south trending Laramie River Forest, <br />located approximately 12 miles to the west. This fault is reported to have a length of 43 <br />miles, to have offset late Tertiary age rocks, and to be overlain by Quaternary age <br />sediments. A second unnamed fa~ is located a similar distance north of the stte. This <br />fault Is east-west trending In the vicinity of Elkhorn Creek and Lone Pine Creek. This fault <br />has a reported length of 6 miles, to have offset Tertiary age rocks, and to be overlain by <br />Holocene age sediments. <br /> <br />5-7 <br />