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.~ ..-t o ..-t ......1 ,-, ~-' Economic and Physical Resources The Grand Valley area of Colorado lies at the junction of the Gunnison River with the Colotado River. The atea was opened to settlement in 1881. The Grand Valley Itrigation Company, started in 1882, dherted water from the Colorado River near the ptesent site of Palisade to irriqate 22,500 acres. From 1889 to 1907, five other small irrigation districts were formed to divert water from the Colorado River to irrigate from a f'=\J hundred to a few thousand acres. The last major irrigation development in the valley was the U. S. Buteau of Reclamation Grand Valley Project started in 1912 to irrigate about 42,000 aCtes. Prior to settlement and the development of irrigation, the valley was described in many reports as very barren with only a sparse cover of greasewood. sagebrush and desert shrubs. . The city of Grand Junction, population 20,170, lying near the center of the irrigated area is the major municipal, corrmercial and industrial area in the Upper Colorado River Basin. In addition to agriculture and retail and wholesale trade, mininq, recreation tourism, government, construction and manufacturing are major sources of earnings. The mean annual temperature at Grand Junction is 520 F. and ranges from a July mean of 780 F. to a January mean of 260 F. The annual precipitation averaqes only 8.29 inches and is rather uniformly distributed throughout the year. The elevation at Grand Junction is around 4,850 feet above SEa level. The averaqe growing season is 190 days. --There are about 80,000 acres of irrigated land in the valley, of which about 11 percent is not cropped in anyone year. The principal crops grown in order of acreage are hay and pasture, corn, fruits, small grain and sugar beets. The average farm size is 50 acres with some as large as 500 acres. Market value from the sale of farm products in 1970 was over $15 million, of which 60 percent is from the sale of livestock, poultry and their prod- ucts and 13 percent is from the sale of peaches, apples, pears and cherries. The soils of this general area are derived from the Mancos Shale formation. This marine formation has a very high salt content and groundwatel' perco- lating over and through the shale picks up high concentrations of salt which are transported to the Colorado River through wasteways, ditches, or by natural groundwater movement to the river. Because of the arid climate, these salts have not been leached naturally, and high quantities remain. Lenses of white crystalline salts are often exposed during excavation opera- tions. The Mancos formation consists of 4,000 feet of relatively uniform s~lt./ clay shale \.lith veinletc I").f gypsum, calcite and sodium sulphate. In past time, the Colorado River has eroded a deep wide channel through the Mancos Shale formation which has since been refilled with alluvial materials to a depth of some 50 to 60 reet The pl'esent channel of the Colorado Ri ver is incised in the anuvicil !'>1[2;o als which are much more permeable th2'1 the shale and serve as a ge:;C?ral iJ:U ;'er fat the floodplain area. Thie" ac,uifer is recharged by deep percolat1on losses from irrigation, canal seepage, and - 1 -