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2 <br /> 2 . 0 Site and Reclamation Elements <br /> 2 . 1 The location of the mine is well inside the isohyet <br /> line encircling an area in Eastern Colorado with less that 14 <br /> inches of annual precipitation. A 40 year period of <br /> recorded precipitation at Fort Morgan averaged 13 . 75 inches <br /> and a 39 year record at Greeley averaged 12 . 60 inches . <br /> Warm-season plants have a decided advantage at <br /> the mine because of the influence of rainfall distribution. <br /> For the largely frost free months , May to September inclusive, <br /> sixty-two per cent of the year ' s precipitation is received <br /> at Greeley, and at Fort Morgan it is 67 per cent. (U . S . D.A. <br /> Yearbook of Agriculture Climate and Man , 1941) <br /> The predominantly summer distribution of preci- <br /> pitation is the primary environmental factor influencing <br /> the dominance of warm-season plants in the native grassland . <br /> Most of the grasses growing in the reference area are warm- <br /> season species . <br /> 2 . 2 Irrigation <br /> Irrigation on reclamation areas is generally bene- <br /> ficial during seed germination and emergence stages . Subsequent <br /> benefits are mainly during extended dry periods. It can <br /> be contended that prolonged irrigation favors heavy growth <br /> of competitive weeds , and possibly, encouragement of <br /> shallow rooting of perennial species wanted in the final <br />