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<br />people are employed in construction, wholesale and retail trade, <br />and public administration. Many Black Hawk residents commute <br />to the Denver metropolitan area to work (Reference 4). <br /> <br />Early development of the city was very rapid due to the discovery <br />of gold in the area in 1859. The limited land available for develop- <br />ment and the large number of people arriving in Black Hawk in <br />a short period caused prompt utilization of almost all the usable <br />property and construction of most of the buildings which remain <br />today. Since about 1890, little new additional construction has <br />taken place due to deteriorating economic conditions. This rapid <br />period of growth resulted in numerous utilizations of the small <br />flood plain area, including railroads, bridges, buildings, mine <br />tailing piles, and roads. <br /> <br />The stream valleys are narrow and steep, being typical of the <br />Front Range mountain area. Elevations within the community range <br />from approximately 7,900 to 9,000 feet. <br /> <br />The headwaters of North Clear Creek originate on the eastern slopes <br />of the continental divide at elevations ranging from 9,000 to <br />over 12,000 feet. The North Clear Creek flows southeasterly until <br />it converges with Clear Creek before emptying into the South Platte <br />River in Denver. Gregory and Chase Gulches are tributaries to <br />North Clear Creek. <br /> <br />Average annual precipitation over the study basin is approximately <br />17 inches, of which over 50 percent occurs in the period of May <br />through August. Mean temperatures range from a high of approximately <br />630F in July to a low of 280F. in January, with an annual mean <br />of approximately 430F. <br /> <br />The basin is vegetated with a typical light-density subalpine <br />covering consisting of Douglas fir, lodgepole pine, ponderosa <br />pine, a sprinkling of aspens, and a sparse grass and brush ground <br />cover. <br /> <br />The soils in the flood plains are moderately coarse-textured gravelly <br />and cobbly alluvium. Soils on south-facing exposures of 40- to <br />70-percent slope are characterized by many outcroppings of feldspars <br />and granite. Soils on north-facing exposures of 35- to 60-percent <br />slope area deep and well drained, medium textured, and are developing <br />from the underlying feldspars and granite. South of North Clear <br />Creek in the higher park areas of 0- to lO-percent slope are soils <br />characterized by rock outcrops and shallow bedrock. These areas <br />are open and are covered with numerous roads and mine pits (Refer- <br />ence 5). <br /> <br />Within the corporate limits of the City of Black Hawk are numerous <br />old abandoned mines and piles of mine tailings. There is always <br />the possibility of soil subsidence and cave-ins from the mine <br />shafts and slippage of the old tailing piles. Pollution in the <br /> <br />4 <br />