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"" o UI ..;;;. CHAP TER I I THE PRICE RIVER BASIN Topography The Price River Basin, located primarily in Carbon and Emery Counties of east-central Utah, has a total drainage area of about 1850 square miles (Figure 1.1). The Price River flows 133 miles in a generally southeasterly direction from Scofield Reservoir and enters the Green River above the town of Green River, Utah. The basin elevation ranges from about 4,200 feet above mean sea level at its confluence with the Green River to 10,443 feet at Monument Peak In the western portion of the bas in. The dominant physiogra) I,:. features of the basin are thg Wasatch Plateau, Book and Roan Cliffs, and the San Rafael Swell. On the west, the Wasatch Plateau rises abruptly from the Price Rivel lowlands to a mean altitude of 9000 feet. "1 t~~ sedimentary heda dip gently away from tlie San Rafael Swell located at the southern end of the basin. The swell is an asymmetrical anti- cline roughly 80 milea long and 30 miles wide. The region is known for its topography of concentric plateaus and massive cliffs. The Book and Roan Cliffa bound the north and east portions of the basin as they extend for 150 miles from West Central Colorado to Castle Gate and then south. Stokes and Cohenour (1956) have described the cliffs as consisting predominantly of shales and sandstone marked by deep canyons and finger- like gravel-capped benches. The weathering gravel caps vary in thickness from 50 feet at the base of the mountains to a thin covering in the valley. . Much of the cap area is cultivated, but production levels on many of the farms have deteriorated because of salt accumulation in the soil. Geology The geology of the Upper Colorado River Basin is the dominant factor determining the occurrence, behavior, and chemical qualities of its water resources (Hyatt et a!. 1970). Surface rocks and soils of marine shale or igin are the predominant source of stream salinity (Mundorff 1972). I I I ~ An extensive marine formation, known as Mancos Shale, has been identified as a major natural contributor of salts to the Colorado River. The formation, which underlies approximately 25 percent (470 mi2) of the Price River drainage, is approximately 5000 feet thick and dips generally concentrically I Non-marine -+- Marine -i- Non-marine . away from the San Rafael Swell. The result is a U-shaped formation (with the top of the U pointing north), 10 miles widg, passing through the lowlands of the Pr ice Ri ver Basin. The Mancos Shale is classified into three main shale members--Masuk, Blue Gate, and Tununk--which generally are separated by sandstone layers (Figure 2.1). In locations where the separating layers of sandstone are missing, the shale is termed "undivided." The Mancos Shales were deposited during the late Cretaceous period by shallow, highly Raline ioLl,,'1 seas (Stokes and Heylman, no date). During the early Cretaceous Period, marine formations were restricted to northern Utah, wh i Ie the non-ma rine Dakota and Cedar Mountain formations were forming in central and southern Utah. When the seas reached Eastern Utah during the Cenomanian epoch, the Mancos Shales were formed. The dominant geologic tendency during this epoch was one of subsidence and shale deposition, but there was at least one intervening period of sand accumulation, represented by the Ferron Sandstone. The clastics formed as the seas were crowded eastward by deposition resulted in complex sequences of near shore sediments, the most important being the Star Point, Garley Canyon, and Emery Sandstone Price River Source Green River formation Colton formation Flagstaff limestone North Horn formation Price River formation Castle Gate sandstone Blackhawk formation Masuk shale Emery, Garley Canyon, and Starpoint sandstones Blue Gate shale Ferron sandstone Tununk shale Dakota formation Cedar Mountain formation Price River Mouth t Mancos Shale formation ! Figure 2,1. Predominant geologic formations of the Price River Basin. 11