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Show PART III IRRIGATION POTENTIAL Mesas, plateaus, and upland plains dissected by occasional deeply entrenched canyons of the river system characterize the lower (desert) portion of the region. Alluvial soils of canyon and valley bottoms and aeolian or residual soils on more remote mesas and plateaus are the most suitable for irrigation where the soil is of sufficient depth and slopes are gentle to moderate. Vast areas of residual soils that are too shal- low or too saline for consideration for agricultural use occur in these desert areas. Topographically, many of the canyon lands bordering the Colorado River and its tributaries are too deeply dissected and eroded for agricultural consideration. Aeolian soils, which are most extensive in the San Juan-Colorado Subregion, are typically coarse to medium tex- tured and occur on a rolling ridge- and swale-type terrain. The narrow swales and other topographic lows are not suitable for irrigation because of an unrectifiable drainage deficiency under irrigation. Potentially irrigable lands range in elevation from 3A00 to 9*500 feet. The northern portion and other mountainous areas are characterized by short, warm summers and long, cold winters. The southern portion and desert areas have long, moderately hot summers and mild winters. The length of the growing season varies from about 70 days in the higher ele- vations and northern portion of the region to more than 200 days in the lower elevations and southern part of the region. The latter will permit a wide crop adaption and increased yields of adapted crops whereas the former will restrict cropping mainly to meadow hay and pasture, similar to the present cropping pattern on irrigated lands. Irrigation practices on newly developed irrigable lands will be com- parable to those now existing on closely associated irrigated lands in the region, as discussed in Part II. It is anticipated that gravity ir- rigation methods will improve and the use of sprinklers will increase as additional lands are developed for irrigation in the future. In this re- port sprinklers are not included in the development and cost tables. It will be essential not only to provide drainage for newly developed areas but also to maintain production on presently irrigated lands by providing additional drainage works, as discussed in Part IV. Water Requirements Water* requirements per acre for potentially irrigable land are ex- pected to be essentially the same as those for presently irrigated lands. Current water requirements reflect the wide variation in climatic condi- tions, soil and topographic conditions, irrigation practices, and the mix of crops grown. Since many of the potentially irrigable lands are inter- spersed and adjacent to irrigated lands, climatic and physical conditions will be similar. It is also expected that irrigated land will continue to be usecl principally for production of crops which support the 60 |
