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Geotechnical Data Report Bruce Park Dam <br />Bowie Resources, Limited <br />0) April 2001 <br />6.2 Site Geology <br />The following paragraphs describe the geology of the glacial till soils and bedrock present <br />below the main dam, saddle dam and reservoir area. A geologic map of the site is provided <br />on Figure 3. <br />Beyond the main dam and saddle dam, the reservoir site is covered by Pinedale-aged glacial <br />till of the Grand Mesa Formation. The Grand Mesa Formation till is predominantly silt and <br />low plasticity clay containing unsorted to poorly sorted, gravel to boulder sized particles. <br />The Grand Mesa Formation is generally lighter in color than other tills in the area. It is rich <br />in sand and silt size particles, and has low plasticity clays due to the presence of sedimentary <br />rocks as a source for the till (Yeend, 1969). The till is generally less than 20 feet thick. <br />Where natural slopes are steep and the till is underlain by claystones of the Ohio Creek <br />Member of the Mesa Verde Group, the till is modified by mass wasting in the form of <br />landslides. <br />The valley beneath the main dam appears to contain Bull Lake aged Lands End Formation. <br />10) The Lands End Formation till is predominantly highly plastic clay and silt containing <br />unsorted, gravel to boulder sized, particles. It is generally brown to dark brown and contains <br />swelling clays. The till is reportedly very compact, with up to 70 percent silt and clay. The <br />till ranges from 40 feet thick to over 200 feet thick in restricted drainages. <br />The bedrock at the site consists of interbedded sandstone, siltstone, and claystone of the Ohio <br />Creek and Barren Members of the Mesa Verde Group. Only bedrock of the Barren Member <br />is exposed at the site. This bedrock outcrops in drainage channels downstream of the main <br />and saddle dams. <br />6.2.1 Dam and Reservoir Foundation <br />While most of the embankment and reservoir areas are covered by younger till of the <br />Grand Mesa Formation, the valley beneath the main dam appears to contain older <br />Lands End Formation. The drilling suggests that about 50 feet of glacial till <br />underlies the main dam embankment near the maximum dam section. The <br />embankment appears to be founded on bedrock at the abutments consisting of the <br />Ohio Creek Member of the Mesa Verde Group. The saddle dam appears to be <br />founded entirely on bedrock of the Ohio Creek Member of the Mesa Verde Group. <br />6.3 Landslide <br />A landslide mass is present along the north (right) side of the reservoir. Based on the <br />topography, the slide mass appears to be approximately 500 feet long and extends from the <br />valley bottom to approximately 700 feet above the north side of the reservoir. The <br />GEI Consultants, Inc. 14 99292 01-04-16 Geolechnical Data Report