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3 II. GENERAL DESCRIPTION ():: THE' BASiN Ph;C!_i ca..!, The Gunnison River Basin encompasses an are~ of aboi.t 8,000 square miles in west central Colorado. It includes al I or major portl0~5 of Gunnison, Montrose, Delta and Ouray Counties and portions of Mesa, Hinsdale, Saguache and San Juan Counties. The Continental Divide forms the east and southeast boundary, and the San Juan Mountains and the Uncompahgre Plateau form the south and southwest boundary. Tn"' north boundary is formed by the Grand Mesa and the Elk Mountains. (See FigLre 1) Elevations range from 4,550 feet at the point where the r;C,n,d",on kive-' flows into the Colorado River, to 14,301 feet above sea level on Uncompahgre Peak at the southern edge of the basin. "The Water and Related Land Resources, Gunnison River Basin, Color'ado" (1962) Type IV study provided the fol lowing subbasin eval~ation areas: Subbasins Ac res Squa re Mil es Upper Gunnison 2,529,700 3,952.6 Lower Gunnison Unit Uncompahgre Smith Fork-Crystal North Fork Subtotal Lower Gunnison 959,400 253,300 802,200 2,014,900 588,200 5, 1 32 , 800 1,499.1 395.8 I ,253,4 3,148.3 Whitewater Tot~l Gunnison Basin 919.1 8,020.0 Climate The mean annual temperature for Lower Gunnison stations is 49.60 F. and 35.40 F. for Upper Gunnison stations. The normal precipitation for four lower Gunnison weather stations is 9.75 inches and 17.61 for three upper basin stations. The report by lorns and Others (1965) indicates areas of greater than 40-inch precipitation for all higher mountain areas on the north, east and south boundaries of the basin. Because of the arid cl imate in the valley, salts have not been leached naturally and high quantities remain. Lenses of white crystalline salts are often exposed during excavation operations. 003050