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saturation of the surficial colluvial soils that theoretically could <br /> occur after an extreme precipitation event , is more critical for the <br /> stability of the waste piles. It was taken into account for the purpose <br /> of the stability analyses described in Section 4.0. <br /> 3.3 Surface Water <br /> 3.3.1 Watershed Description <br /> The Ralston Creek watershed above the mine site and facilities <br /> is mountainous and predominantly forested. The watershed is shown <br /> delineated on Plate 3. The total watershed area above the waste rock <br /> piles is estimated at 38.3 square miles. <br /> Elevations in the Ralston Creek watershed area range from about <br /> 10,500 feet (mean sea level datum) in the western mountains to approxi- <br /> mately 6,950 feet in the creek bed at the downstream portion of the <br /> waste rock piles. The watershed is steep, with the slope of Ralston <br /> Creek averaging about 3 percent in the vicinity of the piles. A sum- <br /> mary of the measured and estimated watershed characteristics is pre- <br /> sented in Table 1 . Vegetative and soil cover characteristics are also <br /> noted in the table. <br /> 3.3.2 General :.limatolo:y <br /> The climate in the region is characterized by dry summers and <br /> cool winter periods. The mean annual precipitation over the Ralston <br /> Creek watershed generally averages about 23 inches (Soil Conservation <br /> Service, 1980) . About 30 percent of the mean annual precipitation <br /> occurs as snowfall . Based upon Soil Conservation Service (SCS) snow <br /> course data for the Baltimore Station, located in Sect. 4, T2S, R73W <br /> (about 5 miles north-northwest of the Ralston Creek watershed, Plate 3) , <br /> the average snow depth on the ground at approximately elevation <br /> - 10 - <br />