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<br />. <br /> <br />10. Lower Gunnison Basin Unit, North fork Area (Reclamation) <br /> <br />.- <br /> <br />ce. The Lower Gunnison Basin Unit-North Fork Area. is located in <br />~ west-central Colorado on the Gunnison River in Delta County. The Gunnison <br />() River is tributary to the Colorado River. The unit area is bounded on the <br />north by Grand Mesa National Forest. on the east by Gunnison National Forest, <br />and on the south and west Jy the Gunnison River. Major communities in the <br />study area include Cedaredge, Crawford, Hotchkiss, and Paonia. The study area <br />includes about 67,750 acres of irrigated land which includes farms, ranches, <br />and orchards. A large portion of the study area is undeveloped land composed <br />of soils derived from the Mancos Formation. Portions of the study area have <br />been investigated by Reclamation for irrigation projects thus providing some <br />information. <br /> <br />The major source of salt in the study area appears to be primarily <br />gypsum from the Mancos Formation and from its soils. The distribution of this <br />salt does not appear to be uniform; one of the objectives to be accomplished <br />early in the study is to identify the highly saline areas. with this <br />information, the study area boundary can be refined for more efficient study. <br />The primary causes of the salt loading appear to be related to irrigation <br />delivery system seepage and applied irrigation percolation through the saline <br />soils; however, a significant amount of salt loading appears to be contributed <br />by nonirrigation (natural) sources due to the large drainage area and the <br />extent to which it is underlain by Mancos Shale soils, abandoned gas, and oil <br />exploration wells. <br /> <br />Although th~s investigation is in its very early stages and salinity <br />studies are in initial stages, an estimated 480,000 tons of salt per year is <br />believed to be contributed from the North Fork area. SCS determined, from its <br />on-farm Lower Gunnison Basin salinity study, that a total of 840,000 tons of <br />salt is contributed from the North Fork area and uncompahgre Valley. <br />Reclamation has completed a study of the Uncompahgre valley and found that <br />about 360,000 tons of salt is contributed from that area; the remaining <br />480,000 tons is assumed to be contributed by the North Fork area. <br /> <br />Preliminary salinity control concepts to be considered for this <br />study include selectively lining canals and laterals and providing piped <br />winter stock water rather than operating canals and laterals year round. <br />Other concepts will be considered as the investigation proceeds. <br /> <br />Water quality and quantity monitoring in surface streams is <br />underway. A contract for aerial photography was completed during the fall of <br />1984 providing information for environmental, hydrosalinity, and engineering <br />studies. A synoptic river survey will be conducted and a river budget <br />completed during the summer of 1986. This data will aid in identifying the <br />highly saline areas within the study area for more detailed study. <br /> <br />11. Lower Virgin River Unit (Reclamation) <br /> <br />This unit is located along the Lower Virgin River in northeastern <br />Clark County, Nevada, and northwestern Mohave County, Arizona. The unit <br />includes natural saline springs averaging 2,900 mg/L near Littlefield, <br />Arizona, and the 3,500 acres of irrigated land along the Virgin River between <br />the springs and Lake Mead. <br /> <br />VII-20 <br /> <br />- <br />