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GEOLOGY AND GEOLOGIC HAZARDS OF THE PROPOSED GOLDEN PEAK RACE TRAINING AREA, VAIL RESORT, SUMMIT COUNTY, COLORADO (Final Revised Report)

A 2300 ft-long, dormant (Quaternary) landslide deposit lies south and west of the proposed new ski trails. This “Big Slide” deposit ranges from 50-80 ft thick, is relatively dry (only 1-3 ft of saturation in the bottom of the slide deposit), and apparently does not possess a low-strength, clayey basal shear plane. Computer slope stability analysis of the Big Slide, using minimum material strengths from borehole samples, indicates surprisingly high Factors of Safety (2.1-2.2 in its present condition, and 1.3 if the water table were to rise to the ground surface). Water table at time of drilling was 39 to 59 ft below surface. The estimated rise due to Spring snowmelt would equate an FOS of ~1.9. We concluded that the proposed Drainage Management Plan would result in groundwater rises very much smaller than needed to decrease current slide stability to failure levels.