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CJ -- ~. . "l:I" - ~- '- FISH AND WILDLIFE SERVICE REPORT .~ -) ". is made up mainly of a series of benches averaging about one mile in width and 100 feet or less in elev~tion differences. 7. Geology.- The geology of the Green River Basin has been influenced greatly by the mountain ranges surrounding the basin, particularly the Uintas which form the southern boundary of the basin. The Uinta Moun- tains extend from the Wasatch Range eastward across the northern part of Utah into northwestern Colorado. They were carved out of a large, simple anticlinal fold of sedimentary rocks arched up into essentially their present altitude at the end of the Cretaceous period. The Uinta Mountain group, a series of brick-red to purplish-red quartzite and sandstone beds of pre-Cambrian age, aggregating more than 12,000 feet in thickness, makes up the central mass of the range. Flanking the quartzite core and sharing its anticlinal structure are bede of lime- stone} sandstone} and shale ranging in age from Upper or Middle Cambrian to Upper Cretaceous. Gently warped Tertiary sediments, mostly of Eocene age, fill the large Green River Basin north of the range to a depth of several thousand feet and lap upon the flanks of the surrounding moun- tains from which they were chiefly derived. These deposits are known as the Wasatch, Green River, and Bridger formations. 8. Soils.- The upper Green River valley lands suitable for agricultural developnent are largely comprised of alluvial soils and are confined to the bottom lands, terraces, and valley fills. They are generally of sandy loam to loam in texture. Mo st of these soils have good natural drainage, provided by light textured soil over gravelly subsoil and a moderate slope. With the exception of small localized arell/3, the soils in the upper valley are free from harmful accumulations of alkali. 9. The soils in the project area are composed Chiefly of Bridger and Green River formations of Tertiary deposition. The Green River deposi~ consist of thin sandstone and limestone beds with thick strata of gray shales. The Bridger formation is composed of dark brown sandstone and varicolored shales. The benches or terraces formed in these materials by lateral stream planation usually have a capping of river sand and gravel over the underlying sandstone or shales. Project soils in most cases have been derived from these river deposits. 10. Climate.- The average annual precipitation near the project area varies from 7.05 inches at Eden to 7.42 inches at Green River, Wyoming. Temperatures vary from a low of .480 F. at Eden to a high of 1030 F. at Green River with frost free periods varying from 89 days at Eden to 100 days at Green River. The January average temperature at Eden is 9.80 F. and 18.50 F. at Green River, while the July average varies from 64.20 F. at Eden to 69.30 F. at Green River. n. Hydrology. - The project would affect ap:llroximately 39 miles of Green River from four miles below La Barge Creek to Big Sandy Creek. The stTSam 2