OCR Text |
Show PART III IRRIGATION POTENTIAL About 375*200 acres or 5 percent of the potentially irrigable land is in Class 1. These lands are suitable for continued high yields of climatically adapted crops under sustained irrigation with minimum costs of development and management. A total of 2,700,900 acres of land or 38 percent of the potentially irrigable land is in Class 2. These lands are moderately productive or require intermediate costs for development and management because of slight to moderate limitations in land characteristics. Approximately 2,Vf5>100 acres or 35 percent of the potentially ir- rigable land is in Class 3« These are lands of restricted productivity for most crops or they require relatively high costs for development and management because of moderate to severe limitations in land characteris- tics. About l,507>^00 acres or approximately 21 percent of the potentially irrigable land is in Class k. These lands have restricted crop adapt- ability because of severe limitations in one or more land characteristics. These limitations include steep or irregular topography with adequate soil for high income crops such as fruit or less favorable soils adapted to low income crops such as pasture. This class also includes marginal lands with adverse soil conditions such as slowly permeable, saline, sodic, or shallow soils which adapt them only to pasture and meadow use. Approximately 63,553*200 acres, comprising more than 90 percent of the total land area of the region, are in Class 6. These are lands with extreme limitations in land characteristics which make them unsuitable for sustained irrigation. The specifications(I) for the above irrigation land classes are pre- sented in Table 20. Irrigation land classes are similar to irrigation soil classes as presented in Appendix VI with respect to permissible ranges of soil prop- erties. The soil classes do not include consideration of on-farm land development such as clearing of brush, trees, and stones, leveling, and drainage. Also, they do not consider such economic factors affecting feasibility of irrigation development as size and shape of tracts or dis- tribution pattern of the lands. The complex physiography and geology of the region are principal factors governing the pattern of occurrence of the potentially irrigable lands shown on subregional maps presented previously. The lands are lo- cated in highly dissected mountainous plateaus, typified by deep canyons, river valleys, rolling ridges, and flat-topped mesas. These are bordered by mountain ranges studded with high, rugged peaks. This highly dissected landscape has been largely scoured and eroded by rivers, streams., and to |