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VII-2 . Sopris. The majority of water originates as snowpack on the northw~st flank of the mountain, an area of high snowfall. This permeable alluvium is underlain by less permeable igneous and sedimentary bedrock which acts as an "acqui tard" and restricts the downward movement of the water into the subsurface. The springs emerge, therefore, where the creeks have eroded down into and exposed the bedrock. Nettle Creek has a 3.7 square mile drainage basin situated on the northwest side of Mt. Sopris. It is tributary to the Crystal River, which in turn is tributary to the Roaring Fork and Colorado Rivers. The basin ranges in elevation from 12,880 feet near the summit of Mt. Sopris, to 6,500 feet where Nettle Creek joins the Crystal River. Much of the upper portion of the basin consists of talus from Mt. Sopris' intrusive igneous formation and has no tree or large plant ground cover. Starting at about 9,000 to 9,500 feet, the basin is covered with various types of vegetation ranging from Scrub Oak to Spruce-Fir stands. . The entire basin averages about 30 inches of precipitation in a normal climatic year with the amount of precipitation falling about equally be- tween the summer and winter months. The average year's runoff at the higher elevation is estimated at 1,400 acre-feet per square mile with about half of it running off during the peak snowmelt period in April, May and June. The dry year unit runoff yield is estimated at 1,000 acre-feet per square mi Ie. Much of the Nettle Creek basin runoff comes in the form of springs which flow year around. These springs are fed by snowmelt and rain that percolates into the porous geologic formation on the sides of Mt. Sopris. Some of the spring water in the lower basin comes from irrigation return flow from the Colpitts o i tCIles . There are no stream gaginCJ stations on Nettie Creek. However, based on several historic measurements on Nettle Creek by Wright-McLaughlin Engineers .