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Era- them "';:: o N o '" OJ U System Series >- ~ ~ .... 0: I:l Table l.--Summary of the geologic formations and groups in the Upper Colorado River Basin and their physical, hydrologic, and chemical characteristics--Continued r, Q 9 T I' V J, Formation and group HYdTO-! ge-o- logic I unit1 I , Physical characte~istics The Uinta and Bridg~t Fotmations consist primatily of claystone aDd some sandatoD~ and minor amounts of shale. The Green River Foraation consists pri- marily of marlstone, shale, oil shale, claystone, silt- stone. and sandstone. These formations together generally are 500 to 2,000 feet thick. ! The Wasatch FOrlDatiop underlies ! the Green River fonnation and , is oO[1lla11y about 1.000 to I 4,000 feet thi~k. The Wasatch consists chiefly of sandy mud- stone, calcareous mudstone, and catbonaceous shale. In the deeper parts of the basin tbe ~asatcb Formation may be as much as 7,000 feet thick. The Fort Union Fo~ation con- sists o,! approxill18tely 1,500 feet of interbedded carbona- ceous shale, sandstone, and coal beds. Hydrologic characteristics Tbe hyd~aulic conductivity of these formations is fairly small, and most wells yield less than 15 gallons per minute. Well yields as much 8S 200 gallons per minute have been reported. Recharge is trom infiltration of precipita- tion and snowmelt. These forma- tioDS are expo5ed for the most part in the lo~-lying arid regions of the basin where the potential for recharge is small. Tbe Wasatch Formation consists pri- marily of fluvial sediments and ~as generally a better water qual- ity than'the lacustrine Green River Fonaation. The Was~tch is a good source of water, and well yields of as mucb as 700 gallons per minute are reported. Recharge i8 from direct infiltration of precipitation and snowmelt. Re- charge also may be from discharge from underlying bedrock aquifers. Recbarge is small to this formation because of the meager precipitation tbat occurs in most areas where tbe {ormation is exposed. Discharge is small and is due primarily to evapo- transpiration and discbarge to streams. Because the ~asatch nor- mally is very thick. there are tre- mendous quaotities of ground water in storage in thi.s formation. Cbemical characteristics The Green River Formation con- tains considerable amount~ of very solubl~ minerals, the most eKteosive being nahco- lite (NaHC03) aDd balite (HaCl). The no~mal range of dissolved-solids conceDtra- tions of ground water from the rocks i6 [rom 1,000 to 3,000 mg/L but locally may be much higher. The Green River and Wasatcb se- quence contributes significaot salt loads to streamflow io the Upper Colorado River BasiD. The dissolved-solids concentra- tiOn of ground water normally is in the range of SOO to 1,500 mg/L but locally may be much gr~ater.