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. f\J .... c.c 00 is usu211y less than 25 gpm and .more often closer to 5 or 10 gpm. The above major formations are cemented mixes of sandstones. silt- stones, and shale materials, Together with the Lewis and Mancos shales, these bedrock aquifers offer a very low hydrologic conduc- tivity, Only a few areas, such as near Craig where sandstone type aquifers confined by impermeable shale units create artesian pressure, yield amounts as high as 100 gpm. Artesian water is often found in the Williams Fork Formation, its underlying unit (the lIes Formation), or in Dakota Sandstone. Most well depths are 200 feet or less (Brogden and Giles, 1977). Bedrock aquifers produce calcium and sodium bicarbonate type water from the dissolution of the sandstone and conglomerate cements or from contact with gypsum; organic materials and coal add calcium carbonate to the water. Table D.l summarizes the more important water quality parameters of each of the geologic units. . The lower Yampa River area (through Dinosaur National Monu- ment) possesses small to moderate quantities of ground water. Primary aquifers include the Browns Park, Morrison, and Morgan formations and the Entrada, Glen Canyon, and Weber sandstones. Wells vary from 300 to 800 feet deep. The Glen Canyon Sandstone produces up to 60 gpm to wells. One well in Echo Park, Dinosaur National Monument (near the confluence of the Green and Yampa Rivers), produced 130 gpm (Sumsion, 1971). Alluvial aquifers along the upper Yampa River gene~al1y provide a more abundant source of water. Well yields range from 5 to several hundred gpm at depths of 8 to 100 feet. The alluvia are relatively thin, typically around 20 feet, but alluvial reserves can be supplemented by streambed flow-through from adjacent aquifers to sustain yields. Water quality depends on the type of parent material, but usually it is slightly alkaline (sodium or calcium bicarbonate) or a calcium sulfate when in contact with Fort Union Formation material. TIle average dissolved solids level is 724 mg/liter (Brogden and Giles, 1977). Outside of the Piceance Creek Basin and the lower White River, little is kno~ of the ground water resources of the White River Basin of Colorado. Inferring from the known hydrologic properties of various geologic units, the area west of Meeker, Colorado, would likely provide sizable (less than 600 gpm) amounts of water from the Williams Fork (Sandstone) and Wasatch (claystone/siltstone/ sandstone) formations (Boettcher, 1972). The Green River Formation surrounds Piceance Creek Basin and extends into the Grey Hills of Colorado; typical well yields are as hiah as 100 gpm or more in this formation (Boettcher, 1972). West of the Yellow Creek-White River confluence lie the Williams Fork and lIes formations, both of which yield moderate amounts of water. I .1 D-11