| Summary: | August 1966. Includes bibliographical references (pages 60-62). Covers not scanned. Print version deaccessioned 2021. The Little South Poudre is one of the larger tributaries of the Cache La Poudre River, which drains approximately 105 square miles on the east flank of the Mummy Range in the north-central Colorado Front Range. The low total dissolved solids content, ranging from 28 to 75 ppm, of the surface water obtained from the region indicates the water is chemically of excellent quality. Starting with snow, the source of virtually all recharge in the region, mineral content increases on the average of 4% times as melt water comes in contact with soil and Precambrian crystallines, then triples again during penetration of the water into the ground-water system as it moves toward perennial springs. Surface and ground water is predominantly of the bicarbonate-silica type with minor amounts of calcium, magnesium, sodium, potassium and other common chemical constituents. For greater effectiveness in interpreting and analyzing water-quality data, the Little South Poudre has been divided into sub-watershed units. Generally, mean values of dissolved mineral concentrations are consistent throughout these basins; however, certain exceptions do occur. In Beaver Creek and the Little South Poudre (mainstem) anomalous iron and copper concentrations, respectively, were recorded. These anomalies can probably be attributed to an iron "fixing" bacteria and zones of copper mineralization, respectively. High concentrations of dissolved solids in ground water feeding Fish and Pendergrass Creeks probably accounts for values of total dissolved solids that were well above the overall mean for the watershed. Fall Creek was selected as a geologic control area for the inorganic water-quality study. The upper Fall Creek portion of the Little South Poudre watershed consists chiefly of a sequence of Precambrian biotite schist, biotite-quartzofeldspathic gneiss, granite and amphibolite. Metamorphic rocks in the area have probably ...
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